Gas-Liquid Falling Film Equilibration System and Methods of Use

ABSTRACT

The current disclosure provides a gas-liquid falling film equilibration apparatus, systems incorporating the apparatus, and methods of their use. The apparatus comprises a chamber, an equilibration member within the chamber, liquid and gas inlet and outlets, such that a liquid introduced into the chamber from the liquid inlet contacts the upper portion of the outer surface of the equilibration member. The apparatus finds use in the measurement of dissolved gases in a variety of liquids including the measurement of carbon dioxide in water.

TECHNICAL FIELD

Systems and methods for determining the concentration of gases inliquids are provided. The systems include an apparatus (equilibrator)having a high surface area that permits gases present (e.g., dissolved)within the liquid to diffuse into an exchange gas, permittingmeasurement of the gases. The systems find use in the measurement of avariety of gases including carbon dioxide (CO₂), methane, radon,hydrogen sulfide, total trihalomethanes, sulfur hexafluoride, nitrousoxide, sulfur dioxide, hydrogen, chlorine and/or bromine and the like.The systems are designed to resist clogging or fouling by suspendedmaterial in the liquids and are particularly useful in themeasurement/monitoring of CO₂ in aqueous systems. The present disclosurealso provides methods for rapidly determining the partial pressure ofvarious gases including CO₂ (pCO₂) in a body of water. The systems andmethods are particularly useful for measuring/monitoring pCO₂ in coastalwaters and other bodies of water where pCO₂ can change rapidly and varywidely at sites that are in close proximity to each other. In additionto their use in coastal/environmental monitoring, the gas-liquid fallingfilm equilibration system described herein can be used in industrial andlaboratory settings where liquid-gas equilibration is needed. Theequilibrators can be connected to a single or to multiple gas detectors(e.g., to measure multiple gas species simultaneously), including butnot limited to analytical instruments such as gas chromatographs, massspectrometers, instruments that perform absorption spectroscopy such asnon-dispersive infrared gas analyzers, laser absorption spectroscopy,and cavity ring down spectroscopy, etc.

BACKGROUND

The measurement/monitoring of gases in various liquids is of bothenvironmental and industrial importance. Various systems for themeasurement of gases, including but not limited to CO₂, have beendevised. Included in those systems are apparatus that assess theconcentration of gases in the liquid directly (e.g., by spectralanalysis or chemical reaction in the liquid phase) and those that forcethe gas from the solution by physical/chemical means (e.g., addition ofacid, elevation of temperature, etc.) thereby permitting measurement inthe gas phase.

Measurement of gases including greenhouse gases such as carbon dioxide(CO₂) and methane are of increasing importance as they have an effect onthe regulation of the earth's temperature. It is estimated that roughly30% of anthropogenic CO₂ leaves the atmosphere and enters the earth'soceans and other large bodies of water. These water bodies typically actas large sinks of CO₂, wherein dissolved CO₂ becomes carbonic acid,carbonate, and bicarbonate, with concomitant changes in pH.Unfortunately, devices for directly measuring pH in the naturalenvironment are unreliable when deployed for any length of time,especially in systems with high productivity and/or sediment loads. Incoastal systems, such as estuaries, where changes in salinity are commonand biofouling extensive, measuring pH can be burdensome and inaccurate.Alternatively, measurements of changes in the partial pressure of CO₂ inthe ocean can provide valuable and reliable information about changes inthe acidity of the ocean. Nearshore coastal water pH measurements canalso be made providing similar information.

Methods for measuring pCO₂ in oceans have mainly focused on measuringacidification in open ocean settings. These methods assume thatacidification is driven by a stable air-sea CO₂ equilibrium, such thatmeasurement of the ocean's pCO₂ is reflective of atmospheric pCO₂. Thetechnology depends on large, expensive, and sparse autonomous buoys tocharacterize hundreds to thousands of km² of ocean surrounding them.Buoy data are supplemented by data from large, expensive, and sparseoceanographic research vessel taken during ocean transits.

Due to the complex make-up of nearshore coastal waters, an air-seaequilibrium rarely occurs and measurements must be made at higherfrequency over space and time. Increased frequencies can assist toreliably characterize pCO₂ and pH. In nearshore waters the carbon cycleis much more complicated than in the open ocean, and land-seainteractions and ecosystem metabolism are frequently more acute driversof pCO₂ than air-sea interactions. Nearshore waters are furthercomplicated by biological activities such as photosynthesis andrespiration and the pCO₂ of the water is far more dynamic than in theopen ocean. Changes in pCO₂ are more rapid than in open ocean waters andpCO₂ can vary significantly over very short distances and time spans.Measurements must therefore be made much more frequently and much moredensely in order to capture the natural temporal and spatial variabilitypresent.

Challenging environmental conditions also adversely affect the accuratemeasurement and long term monitoring of other gases that dissolve inwater (e.g., radon, methane, etc.)

Accordingly, the development of measurement devices that are reliableenough to operate for significant periods of time without maintenance(e.g., resistant to clogging, freezing, and fouling) and which arecapable of supporting suitably accurate assessments of gases in variousliquids, including the waters of oceans, lakes, rivers, and streams, isuseful for environmental, industrial, and residential purposes.

SUMMARY

The present disclosure describes an gas-liquid equilibration apparatuscomprising:

-   -   a chamber comprising an outer wall that is disposed        substantially symmetrically about a central axis, the outer wall        defining the interior surface of the chamber, the exterior        surface of the chamber, and space within the chamber;    -   an equilibration member within the chamber having an        equilibration member surface, an axis of rotation, and a        bisecting plane perpendicular to the axis of rotation positioned        at the midpoint of the equilibration member's axis of rotation;    -   the equilibration member being positioned within the chamber        such that its axis of rotation and the central axis of the        chamber coincide or substantially coincide;    -   the chamber, the exterior surface of the chamber, the interior        chamber wall, the equilibration member within the chamber, and        the space within the chamber being divided into an upper portion        above the bisecting plane and a lower portion below the        bisecting plane;    -   the space within the upper portion of the chamber being in        liquid (fluid) and gas communication with the space within the        lower portion of the chamber via one or more gaps between the        equilibration member and the chamber wall;    -   at least one liquid inlet located in the upper portion of the        chamber positioned such that a liquid introduced into the        chamber from the one or more liquid inlet contacts the upper        portion of the outer surface of the equilibration member;    -   at least one liquid outlet located in the lower portion of the        chamber positioned to permit outflow of some or all of the        liquid introduced into the chamber that collects in the lower        portion of the chamber by gravity;    -   at least one gas inlet located in the wall of the lower portion        of the chamber; and    -   at least one gas outlet located in the wall of the upper portion        of the chamber;        wherein at least a section of the upper portion of the chamber        wall is removably-resealable to the remainder of the upper        surface and/or the outer wall.

This disclosure also provides for methods of determining the amount of agas (or gases) of interest present in a liquid using an apparatus asdescribed herein comprising the following steps:

-   -   i) providing an apparatus;    -   ii) introducing the liquid into the chamber of the apparatus by        way of the liquid inlet(s) such that it passes over the        equilibration member thereby forming a film over all or part of        the equilibration member's surface, and exits the apparatus by        way of the liquid outlet(s);    -   iii) directing a carrier gas into the apparatus by way of the        gas inlet(s) such that it flows over the equilibration member        (the liquid film running down the surface of the equilibration        member) in a direction that is counter current to the flow of        the liquid and exits the chamber of the apparatus by way of the        gas outlet(s);    -   iv) directing all or part of the gas that exits the chamber to        at least one sensor of an analytical instrument that determines        the amount of the gas (or gases) of interest present in the gas        that exits the chamber.

Accordingly, the concentration of the gas of interest in the gas exitingthe chamber can be used to determine the amount of a gas (or gases) ofinterest present in the liquid based on the output of the detectionsystem.

Tests of the falling film liquid-gas equilibrators described hereinacross broad ranges of gas (e.g., CO₂) concentrations, liquid (e.g.,water) and carrier gas (e.g., air) flow rates indicate that falling filmequilibrators as described herein have the ability to produceconsistent, precise, and accurate dissolved gas measurement (e.g.,dissolved pCO₂ measurements) even across significantly differentequilibrator dimensions.

The apparatus may be used to determine the concentration of a variety ofgases in a diverse number of liquids, including the concentration ofcarbon dioxide in aqueous systems (e.g., fresh or salt water).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration introducing the general terminology for thefalling film gas liquid equilibrators described herein using anequilibrator with a substantially cylindrical chamber having a height hat the central axis cax (

), an inner radius r, an outer radius R, and a wall w of thickness t.The equilibrator is shown as having a substantially sphericalequilibration member em with an axis of rotation axr (

) having a length substantially equal to the height of the em, and amaximum radius emr, appearing, in this instance, at the equator e of thesphere. As the emr is less than the inner radius r, a gap g is shownbetween the inner surface of the w and the surface of the em. In theillustration the cax and the axr are substantially aligned. The drawingis not to scale.

FIG. 2 shows a schematic cutaway of an equilibrator with a substantiallycylindrical chamber with a wall w showing its spherical equilibrationmember em and a gap g between w and em. The schematic shows the liquidinlet 1, liquid outlet 2, gas inlet 3, gas outlet 4, liquid is denotedby the wavy lines

and gas by the dashes

.

FIG. 3 shows a schematic cutaway of an equilibrator with a substantiallycylindrical chamber and a spherical equilibration member as in FIG. 2.As diagramed, the planar upper surface of the cylinder 5 has a lip 6 andis removably-resealable to (against) the cylindrical wall, at location 7(via e.g., an o-ring). In such an embodiment, the planar upper surfaceacts like a substantially air-tight/water-tight “lid” on the cylindricalchamber. The annular support as supporting the equilibration member isshown below the level of liquid (e.g., water) in the chamber.

FIG. 4 shows a schematic cutaway of an equilibrator with a substantiallyellipsoidal chamber and an ellipsoidal equilibration member. Holes,gaps, or channel in the annular support as permit liquid introducedthrough inlet 1 to reach the liquid outlet 2.

FIGS. 5A-5N show generalized cross sections of equilibration membersincluding 5A spherical, 5B ellipsoidal, 5C ovoidal, 5D fusiform shape,5E hemisphere, 5F hemiellipsoid, 5G hemiovoid, 5H domed frustum (domedfrustoconical section), 5I domed vertical right column, 5J column havingoscillating sides (e.g., sinusoidal changes in the column radius), 5Kcone having sinusoidal oscillating sides (column with sinusoidal changesin the column radius), 5L a series of spheroids or discs, 5M fourspheroids, and 5N a series of spheroids or disc of increasing size.

FIGS. 6A-6N show generalized cross sections of equilibratorsincorporating the equilibration members shown in FIG. 5. Eachequilibrium member is shown in an equilibrium chamber having a liquidinlet 1, a liquid outlet 2 a gas inlet 3, and a gas outlet 4 indicted byarrows.

FIGS. 7A and 7B show in 7A a gas inlet nozzle 100, and in 7B a gasoutlet with a shield 101. The inlet and outlet are shown in a portion ofchamber wall 102 and are held in place by a retaining nut 103 thatengages threaded section 104. When fully tightened, nut 104 causescompression of seal 105 providing a substantially gas and liquid tightseal. The nozzle shown in FIG. 7A has an internal pathway 110 throughwhich gas may enter the chamber and be dispersed through nozzle end 120.The gas outlet shown in FIG. 7B has a shield section 101 that preventsdroplets of liquid (e.g., water) from entering the entrance of the gasoutlet 130, which is in gas communication with the internal passage 140that forms part of the gas outlet.

FIG. 8 shows a schematic of one configuration of a system thatincorporates equilibrator (E). Various components of the system may beconnected by wires or wireless communication components that are notshown. In addition, the sensor(s) (13) need not be encased in theanalytical instrument.

FIG. 9 shows a performance comparison of equilibrators having an 8-inchdiameter spherical equilibration member with an equilibrator having a10-inch dimeter equilibration member over a 6-day period in a dynamicpCO₂ test as described in Example 1. Measurement values taken from theequilibrator having an 8-inch diameter spherical equilibration memberare shown as a filled dot “•”, and those taken with the equilibratorhaving a 10-inch dimeter equilibration member are shown as an opencircle “◯”. Similar results are obtained down to about 3.7-inch diameterspherical equilibration members.

FIGS. 10A-10F show six photographs of a spherical falling filmequilibrator apparatus of the type shown schematically in FIG. 3 andused in Example 1 (10-inch diameter equilibration member) having a 13.25liter chamber that is substantially a virtual right cylinder (VRC): FIG.10A, fully assembled for operation; FIG. 10B, opened to show theequilibration member with the view from above; FIG. 10C, showing arubber or plastic seal along the upper edge and an annular supportwithin the chamber, the gas inlet is visible in the photo about 4'oclockon the chamber wall; FIG. 10D, the equilibrator with a 3.7-inch diameterequilibration member and a 0.565 liter chamber; FIG. 10E, side by sidecomparison of a 6-inch diameter equilibration member and a clear 4 literchamber (left) and an 8-inch diameter equilibration member and a 7.57liter chamber (right); FIG. 10F, side by side comparison of a 3.7-indiameter equilibration member in clear 1 liter chamber (left) and an8-inch diameter equilibration member and 7.57 liter chamber (right).

FIGS. 11A-11F are photos providing the basis for FIGS. 10A-10F.

DETAILED DESCRIPTION Definitions

An equilibrator is an apparatus for contacting a gas and a liquid so asto exchange one or more gases between the phases. The term equilibratordoes not mean the apparatus brings the two phases (gas and liquid)necessarily into perfect equilibrium, but rather brings the phases to astate approaching equilibrium or a dynamic equilibrium so that theamount and/or relative changes in the amount of gases/volatile materialsin the liquid can be determined.

A liquid inlet is a point in the surface of the chamber wall whereliquid enters the chamber. The liquid inlet may terminate at or be inthe form of a nozzle.

A nozzle is an extension or projection at the gas inlet or liquid inletthat directs the flow of gas or liquid within the chamber. Liquid inletshave an opening with a minimum inner diameter to avoid plugging andpromote complete wetting of the equilibrium member, thereby optimizingthe generation of a falling film gas exchange surface.

“Amount” of a gas or gases as used herein may be expressed by anysuitable measure including concentration in the form of molarity, weightper volume (e.g., volume of carrier gas), volume/volume (e.g., pervolume of carrier gas, or percent volume of carrier gas), partial weightor mass (grams gas of interest/gram of gas or liquid, such as ppm byweight), part per million by volume (ppmv), or partial pressure.

Calibration gas or calibrator gas is a gas having a known amount of thegas of interest.

Carrier gas as used herein is a gas, other than the gas of interest,that is passed through the equilibrator and into which the gas ofinterest diffuses, and which may be subject to analysis to determine theamount of the gas of interest present.

The term, “removably-resealable,” as used herein means capable of beingremoved from a location on an object (e.g., the equilibrator chamberwall) and replaced in that location to form a seal. More specifically,with regard to a section of the chamber wall, removably-resealable meansthat a section of the chamber wall can be removed to provide access tothe interior of the chamber and then replaced and sealed sufficiently tothe remainder of the chamber wall to permit operation of the apparatus(e.g., without loss of carrier gas or liquid from the chamber that wouldinterfere with its operation).

Ellipsoidal as used herein means having the form of an ellipsoid.

Ovoidal as used herein means having the form of an ovoid (e.g., eggshaped).

Spheroidal as used herein means having the form of a sphere or spheroid.

Vertically stacked equilibration member(s) means equilibration membersformed from a series of element having an axis of rotation that whenaligned vertically in the equilibration chamber each have their axis ofrotation substantially aligned with the central axis of theequilibration apparatus. See. e.g., FIGS. 5A through 5N.

Description

The measurement of CO₂ and other gases or volatile materials present inliquid (e.g., aqueous) samples may be conducted using a variety oftechniques. In many techniques the gas(es) of interest areremoved/forced out of the liquid for measurement in the gas phase. Thegas phase may include a carrier gas or mixture of carrier gases intowhich the gas(es) of interest in the liquid move (e.g., exchange or areadded to the carrier gas(es)). The movement of gases out of the liquidmay be accomplished by a number of processes including, but not limitedto, alteration of the chemical composition of the liquid (e.g.,acidification), reduction of the pressure, and passive diffusion. Avariety of different equilibration apparatus or “equilibrators” has beendeveloped with the goal of efficiently exchanging/equilibrating thegases in the liquid phase with a carrier gas that is in turn directed tothe sensor of a detection/analysis instrument (gas analyzer) formeasurement of the gases of interest. Among the equilibrator designs arethe “shower type”, “bubble Weiss type”, and “laminary flow type”described by Frankignoulle et al. (Water Res. Vol. 35, No. 5, pp.1344-1347, (2001)). While each of such systems may be useful, theysuffer from a variety of disadvantages including, but not limited to,the inability to handle materials with suspended particles,susceptibility to fouling (e.g., biofouling), difficulty in removal ofdeposits (cleaning) built up by suspended particles and/or fouling, andinstability when subject to tipping or motion during measurement.

The present disclosure describes, and provides for the use of, a fallingfilm type of equilibrator that provides a rapid response time that isgoverned by the dead time (i.e. time after a change to the input beforeits initial detection) and the lag time (i.e. how fast theequilibration/detection process proceeds), the specific values of whichdepend on the specifics of the equilibrator design and the detectioninstrument that is being used. The time constant tau (τ), also known asthe e-folding time, is the time necessary for an instrument to respondto an induced step change. τ=1/e decay in concentration (n τ=time atwhich C_(t)/C₀=1/e^(dn); e.g., 3 τ=time when C_(t)/C₀=1/e³) when stepchange is from high to low. Conversely, when the step change is from lowto high concentrations, the response is given by n τ=time whenC_(t)/C₀=1-1/e^(n). For spherical falling film equilibrators describedherein (e.g., with equilibration member diameters of around 3.5 to10-inch diameters), τ ˜3 minutes and 3 τ (i.e. to reach 95% response) ˜8minutes for small diameter equilibrators for carbon dioxide steps fromabout 100 ppmv to about 50,000 ppmv. For an equilibrator having a VRCchamber with a volume of about 7.57 liters and a spherical equilibrationmember about 8 inches (20 cm) in diameter operated at a water flow ratein the range of 225-380 liters per hour and a one (1) liter/minutecarrier gas (air) flow rate, τ can be as low as about 3 to 4 minutes,although it may be longer (e.g., about 4 to about 6 minutes, about 6 toabout 8 minutes, or about 8 to about 9 minutes) depending on theparticular operating conditions. The dead time (time from the initiationof the step change in dissolved gas until the detectors first respond)for such an equilibrator operated under the same conditions is generallyless than about 1 minute. For equilibrators where the head space hasbeen minimized, the response time for carbon dioxide measurements may beless than 3 minutes (e.g., less than 2.5, 2.0, 1.5 or 1.0 minutes, or ina range from 1.0-3.0 minutes, 1.0-2.0 minutes, or 2-3 minutes).Similarly, dead times can be less than one (1) minute (e.g., less than50 seconds, 40 second, 30 seconds, or 20 seconds, or in a range from 20seconds to 1 minute, 20-40 seconds, or 40 seconds to 1 minute).

In a first embodiment the equilibrator comprises a chamber formed of awall w having a liquid inlet 1 and liquid outlet 2 subject tomeasurement; an equilibration member em enclosed within the chamber; anda gas inlet 3 and gas outlet 4 for a carrier gas such that the carriergas flows substantially counter current to the flow of liquid throughthe chamber. The equilibration member has a surface over which theliquid can form a film over all or part of the surface area (e.g., overgreater than 50, 60, 70, 80, 90, or 95% of its surface area) where flowis not inhibited or impeded by the shape or the design or equilibratororientation). In such an embodiment the equilibration member may bewettable by the liquid (e.g., the equilibration member is hydrophilicand the liquid is aqueous). In embodiments, the equilibration member ishydrophilic and the contact angle of the equilibration member with wateris less than about 90°, less than about 80°, less than about 70°, lessthan about 60°, less than about 50°, less than about 40°, less thanabout 30°, less than about 20°, or less than about 10°, as measured by agoniometer at 22° C.

In an aspect of the first embodiment (second embodiment) theequilibrator comprises:

-   -   a chamber comprising an outer wall that is disposed        substantially symmetrically about a central axis, the outer wall        defining an interior surface of the chamber, an exterior surface        of the chamber, and space within the chamber;    -   an equilibration member within the chamber having an        equilibration member surface, an axis of rotation, and a        projected bisecting plane bp that is perpendicular to the axis        of rotation, the bp positioned at the midpoint of the        equilibration member's axis of rotation (e.g., where the em is a        sphere the bp would pass through its equator);    -   the equilibration member being positioned within the chamber        such that its axis of rotation and the central axis of the        chamber coincide or substantially coincide (e.g., substantially        align);    -   the chamber, the interior and exterior surface of the chamber,        the chamber wall, the equilibration member within the chamber,        and the space within the chamber being divided into an upper        portion above the position of the bisecting plane and a lower        portion below the bisecting plane;    -   the space within the upper portion of the chamber being in        liquid and gas communication with the space within the lower        portion of the chamber via one or more gaps between the        equilibration member and the chamber wall;    -   a liquid inlet located in the upper portion of the chamber        positioned such that a liquid introduced into the chamber from        the liquid inlet contacts the portion of the equilibration        member located in the upper portion of the chamber;    -   a liquid outlet located in the lower portion of the chamber        positioned to permit outflow of some or all of the liquid and        suspended solids (e.g., sediments, detritus, phytoplankton,        etc.) introduced into the chamber that tend to collects in the        lower portion of the chamber by gravity;    -   a gas inlet located in the wall of the lower portion of the        chamber; and    -   a gas outlet located in the wall of the upper portion of the        chamber.

During operation the liquid (e.g., water) draining out of the outletforms a seal such that gas may not enter or exit the chamber.Importantly, this seal will self-correct internal pressure to matchambient atmospheric pressure (i.e. if either positive or negativepressures begin to the develop inside the equilibrator chamber, the sealwill be momentarily broken, allowing inside and outside pressure toequalize, with little or no effect on carrier gas-liquid (e.g.,air-water) equilibration. In such an embodiment, at least a section ofthe upper portion of the chamber wall may be removably-resealable to theupper portion of the exterior surface of the chamber and/or the upperportion of the chamber wall.

In an aspect of the first embodiment (a third embodiment) theequilibrator comprises:

-   -   a chamber comprising an outer wall that is disposed        substantially symmetrically about a central axis, an upper        surface, and a lower surface, that together define an interior        surface of the chamber, an exterior surface of the chamber, and        space within the chamber;    -   an equilibration member within the chamber having an        equilibration member surface, an axis of rotation, and a        bisecting plane perpendicular to the axis of rotation (e.g., an        equilibration member substantially spheroidal, ellipsoidal,        ovoidal, or other shape discussed below, see also FIGS. 5A-5N        and 6A-6N), with the bisecting plane positioned perpendicular to        the axis of rotation at the midpoint of the equilibration        member's axis of rotation;    -   the equilibration member being positioned within the chamber        such that its axis of rotation and the central axis of the        chamber coincide or substantially coincide such that the        bisecting plane of the equilibration member is substantially        perpendicular to the central axis of the chamber;    -   the chamber, the exterior surface of the chamber, the chamber        wall, the equilibration member within the chamber, and the space        within the chamber being divided into an upper portion above the        position of the bisecting plane and a lower portion below the        bisecting plane;    -   a liquid inlet located in the upper portion of the chamber        positioned such that a liquid introduced into the chamber from        the liquid inlet contacts the portion of the equilibration        member located in the upper portion of the chamber;    -   a liquid outlet located in the lower portion of the chamber        positioned to permit outflow of some or all of the liquid        introduced into the chamber that collects in the lower portion        of the chamber by gravity;    -   a gas inlet located in the lower portion of the chamber; and    -   a gas outlet located in the upper portion of the chamber;        wherein at least a section of the upper portion of the chamber        is removably-resealable to the remainder of the upper surface        and/or the outer wall.

In such an embodiment, at least a section of the upper portion of thechamber wall may be removably-resealable to the upper portion of theexterior surface of the chamber and/or the upper portion of the chamberwall.

In any of the first, second or third embodiments recited above, thechamber may be a vertical right cylinder. In some embodiments, thesection of the upper portion of the chamber wall that isremovably-resealable to the upper portion of the exterior surface of thechamber, and/or the upper portion of the chamber wall, may be the planarupper surface of the cylinder 5 or a portion thereof. In such anembodiment, the planar upper surface may have a lip 6, which sealsagainst the chamber wall at, for example, location 7, so that it actslike a “lid” on the cylinder of the chamber. The seal at location 7 inFIG. 3 is shown as an o-ring; however, other types of seals may beemployed alone or in addition to o-rings, including compression sealsand snap fit lids. See, e.g., FIG. 3. The liquid inlet 1 and/or gasoutlet 4 may be positioned in the planar upper surface, and either orboth may be positioned in a portion of the planar upper surface that isremovably-resealable to the remainder of the chamber.

In other embodiments, including the first, second or third embodimentsrecited above, the chamber is not a vertical right cylinder. In suchembodiments, the chamber may be a shape, such as an ovoid, ellipsoid, orspheroid, that more closely conforms to the shape of the equilibrationmember leaving a lower headspace volume that will shorten the overallresponse time of the equilibrator to changes in the gas content of theliquid introduced for sampling.

Various features and components of the equilibrators described hereinare discussed in further detail below (e.g., the shape of theequilibration member and/or chamber, material for constructing theequilibrator, and placement of inlets and outlets).

The use of the falling film equilibrators having the above-mentioneddesigns, which are further described herein, and particularly those withspheroidal, ellipsoidal and ovoidal equilibration members offers avariety of advantages. Such equilibrators offer the ability to form andsustain a reliable and effective thin layer falling film. Because thedesign uses an equilibration member centrally located in the chamber,the orientation and/or disturbance of the equilibrator (e.g., placementon a non-level surface or movement on a boat or floating platform) isfar less critical to its successful operation than falling filmsgenerated on other surface geometries such as vertical tubes or planarsurfaces). This is especially true for embodiments where theequilibration member has a spheroidal, ovoidal, or ellipsoidal surfacefor falling film generation. This contrasts with vertical falling filmsused, for example, in industrial applications such as falling filmevaporators that contain hundreds of individual vertical tubes that canbe several stories tall. These systems are stationary as they need toremain plumb to the ground for effective use as they are prone tosuboptimal flow or failure if disturbed or deviated from a verticalposition. In addition, vertical tube equilibrators must be engineeredand built to higher tolerances than the equilibrators described herein.Furthermore, the mechanism for introducing liquid at the tops ofvertical tube-type equilibrators must be properly designed, and the flowcarefully controlled, if sustained falling films are to be maintained.

In contrast, given adequate water flow rate, the falling film designdescribed herein has the advantage of maintaining a sustainably wettedsurface for gas exchange (e.g., fully wetted or greater than 50%, 60%,70%, 80%, 90%, or 95% wetted), even when the water intake is tilted upto nearly 45° from vertical. Thus, physical disturbances and non-plumbplacements do not affect the generation and maintenance of falling filmsand, by extension, do not disturb the proper function of the air-waterequilibrator.

The equilibrators described and provided for herein (e.g., those withspherical, ellipsoidal, or ovoidal equilibration members) also offersome distinct advantages over shower, so-called marble laminary flow,bubbling, and membrane equilibrator designs. Each of those designs hasnarrow passages that are prone to clogging (blockage) and/or fouling(buildup of deposits). Clogging and fouling may have a variety ofsources including sediments, suspended particles, deposition of mineralsfrom the liquid, phytoplankton, detritus, biofouling by marine and/oraquatic organisms (e.g., barnacles, bryozoans, hydroids, etc.), andcombinations of any two, three or more thereof.

Clogging and/or fouling can easily compromise water flow and operationof air-water equilibrators. For example, equilibrator designs thatemploy a showerhead to create water droplets/mists will cease tofunction with even minor clogging/fouling, as will equilibrators thatemploy air stones or frits (which foul from materials in the liquid)that are used to introduce carrier gases into bubbling equilibratorsLikewise, sediments and phytoplankton can clog the interstices amongmarbles in vertical laminary flow equilibrators, thereby compromisinggas exchange. Trapped organic material and organisms can also promotebiogenic processes that affect gas concentrations inside theequilibrator (e.g., respiration and photosynthesis). Clogging andbiofouling greatly reduce the utility of these equilibrator designs,particularly where eutrophic and/or turbid aqueous samples are beinganalyzed. This includes eutrophic and/or turbid samples of water fromcoastal oceans, estuaries, lagoons, rivers, streams, lakes, reservoirs,and the like.

The falling film equilibrators described and provided for herein (e.g.,those with spheroidal, ellipsoidal, and ovoidal equilibration members)use relatively large and difficult to clog water ports that provideunimpeded free flowing liquid (e.g., water) to form the falling film. Assuch, they avoid narrow channels or paths for liquid flow that are proneto blockage by clogging and fouling. In some embodiments, anti-foulingcoatings (e.g., marine anti-fouling paint with, for example, copperincorporated) can be used on the surface of the equilibrator. Inaddition, the internal walls of the equilibrator chamber and fittingscan be coated with anti-fouling treatments, coatings or paints tofurther prevent biofouling. In an embodiment at least the inner surfaceof the chamber is coated with a hydrophobic coating, or hydrophobic andoleophobic coating, that resists fouling. In addition, the nature of theliquid flow through the chamber tends to sweep/carry particulate matteroff the equilibration surface and out of the chamber, preventingbuildup.

In addition to being resistant to clogging and fouling, the sphericalfalling film equilibrators described and provided for herein (e.g.,those with spheroidal, ellipsoidal, and ovoidal equilibration members)are comprised of a very few parts that may be made of durable materialsthat can withstand impact (e.g., durable plastics, or stainless steel).In embodiments described herein, the equilibrator comprises a section ofthe chamber that is easily removed, thereby opening the chamber andpermitting the apparatus to be quickly cleaned by hand in the field. Inan embodiment the section of the chamber wall that is removable is ofsufficient size to permit the equilibration member to be removed. Theremovable section of the chamber wall is designed to be placed back inposition and sealed to the remainder of the chamber (aremovably-resealable section).

As the equilibrators described and provided for herein do not rely onsmall orifices, channels, or interstices for gas exchange and properfunction, the cleaning and maintenance of the equilibrators areminimized and can be performed far less frequently than for thetraditional air-water equilibrators described above. As such, theequilibrator design can be deployed in the field for much longer periodsof time between maintenance checks.

1. Equilibration Members

The equilibration member, which is disposed inside of the chamber of theequilibration apparatus, provides a surface upon which the liquidsubject to measurement (e.g., water or salt water) forms a film as itpasses over the surface and is drawn downward by gravity. Theequilibration apparatus described herein may employ equilibrationmembers in a variety of shapes and sizes. The equilibration members aregenerally symmetrical about a central axis, which extends from the topto the bottom of the equilibration member, and as indicated below isused to center the member within the chamber. As a matter of locating,among other things, liquid inlet(s), liquid outlet(s), gas inlet(s) andgas outlet(s), the equilibration member may be understood to be dividedinto an upper portion and a lower portion by a bisecting plane that isprojected substantially perpendicular to the central axis at themidpoint between the top and bottom of the equilibration member.

In various embodiments the shape of the equilibration member issubstantially a spheroid, an ellipsoid, an ovoid, a fusiform shape, ahemisphere, a hemiellipsoid, a hemiovoid, a domed frustum, a domedcolumn, a column having oscillating sides (e.g., sinusoidal changes inthe column radius), a cone having sinusoidal oscillating sides(sinusoidal changes in the column radius), or a series of spheres ordiscs (two, three, four or more) aligned along a central axis. See FIGS.5A-5N. Any of the foregoing may have one, two, three, four or morespiral grooves along the surface to increase the surface area of theequilibration member.

Where the equilibration member is in the form of a hemisphere, ahemiellipsoid, a hemiovoid, or a domed frustum, the equilibration membermay be formed against or as part of the lower portion of the chamberSee, e.g., FIGS. 6E-6G.

In one embodiment the equilibration member is substantially spheroidal,ellipsoidal or ovoidal. In such an embodiment the equilibration membermay be a sphere, ellipsoid, or ovoid.

In an embodiment the equilibration member is substantially spheroidal.

In an embodiment the equilibration member is substantially ellipsoidal.

In an embodiment the equilibration member is substantially ovoidal.

The equilibration member may occupy a volume that is greater than 50%,60%, 70%, 75%, 80%, 85%, 90%, or 95% of the interior volume of thechamber (e.g., from 50% to 70%, from 60% to 80%, from 70% to 90%, from80% to 95%, or from 90% to 95%). In an embodiment, where the chamber issubstantially a virtual right cylinder (VRC), the equilibration membermay occupy greater than about 50%, 60%, 70%, 75%, 80%, 85%, 90%, or 95%of the interior volume of the chamber. In another embodiment, where thechamber is substantially a VRC, and the equilibration member isspheroidal, the volume of the equilibration member is less than about70% of the interior volume of the chamber (e.g., less than 65%, 60%,50%, 40% or 30% of the interior volume of the equilibration chamber).

As discussed above, the equilibration member may have a surface overwhich the liquid can form a continuous film over all of its surfacearea, or the liquid can form a continuous film over greater than 50%,60%, 70%, 80%, 90% or 95% of its surface area (e.g., flow is not impededby the shape of the design). In such an embodiment the equilibrationmember may be wettable by the liquid. In an embodiment, where the liquidsubject to measurement is an aqueous liquid, the equilibration member ishydrophilic. In such an embodiment, the contact angle of theequilibration member with water can be less than 90°, 80°, 70°, 60°,50°, 40°, 30°, 20°, or 10° measured by a goniometer at 22° C.

The equilibration members themselves may be made from a variety ofmaterials and may be, for example, hollow, solid or made of a shellfilled with another material. Where a shell type structure is used, theequilibration members may be filled with a foam or foam-like material(e.g., a polyurethane foam) having a closed or open cell structure.Where equilibration members are hollow, they are designed to be totallysealed, or sealed sufficiently that only an insubstantial amount of gasor liquid can enter the member's interior space(s). For example, ahollow equilibration member may have a small hole (e.g., pin hole) toprevent pressure differences with the gas and/or liquid within thechamber.

2. Chambers

The chamber of the equilibration apparatus can serve a variety ofpurposes including positioning and supporting the equilibration memberand the gas and liquid inlets and outlets. The chamber may have anysuitable shape provided it does not interfere with the passage of gasthrough the chamber or the formation or movement of the falling film ofliquid introduced into the chamber as it is drawn downward by gravityover the surface of the equilibration member. The chamber comprises anouter wall having a thickness t, with the wall defining the interiorsurface of the chamber, the exterior surface of the chamber, and spacewithin the chamber. In various embodiments the chamber wall is disposedsubstantially symmetrically about a central axis and may have acylindrical, spheroidal, ellipsoidal or ovoidal shape. Where the chamberis spheroidal, it may be a sphere, or it may have a prolate or oblatespherical shape. Regardless of exact shape of the chamber, forminimization of response dead time and rapidity of the response timeheadspace will be closer to optimization when the chamber's interiorsurface is substantially parallel to, or substantially follows thecontour of, the equilibration member's outer surface.

As discussed above, although the chamber may have a variety of shapes,where the chamber substantially conforms to the shape of theequilibration member, the headspace (volume) within the chambersurrounding the equilibration member and the film of falling liquid isminimized. Minimizing the space within the chamber around theequilibration member permits the equilibrator to more rapidly respond tochanges in the gas content of the liquid in the falling film. Theimproved response time is a function of, among other things, the morerapid turnover of the gas within the chamber at any given carrier gasflow rate and the smaller volume of gas into which the incoming carriergas will be mixed with/displace. The response time can also be improvedby limiting areas within the chamber that may form eddies or interferewith the laminar flow of carrier gas from the gas inlet to the gasoutlet. Accordingly, in embodiments, both the equilibration member andthe chamber may have a shape that is spheroidal, ellipsoidal, orovoidal.

In an embodiment, the chamber is in the form of a VRC. Where the chamberhas the overall shape of a VRC, the equilibration member housed withinit may be of any shape discussed above including spheroidal. Where thechamber is in the form of a VRC, and it is desirable to minimize thespace around the equilibration member, the equilibration member may havean ellipsoidal, an ovoidal, or a prolate or oblate spheroidal shape.

Regardless of its shape, the chamber, the exterior surface of thechamber, the chamber wall, the equilibration member within the chamber,and the space within the chamber may be conceptually divided into anupper portion and a lower portion. The upper portion is defined as thesection above the level of the equilibration member's bisecting planeand the lower portion as the section below that bisecting plane when theequilibration member is located within the chamber in position for theapparatus to operate such that its axis of rotation and the central axisof the chamber coincide or substantially coincide.

The chamber may be formed with a chamber wall section that isremovably-resealable to permit access to the interior of the chamber.The section may be of sufficient size to permit access for monitoring,cleaning and maintenance, or even removal of the equilibration memberfor inspection, cleaning and/or replacement. The seal may be anysuitable type, including those formed by o-rings, gaskets, snap-fit,compression or frustoconical sections (e.g., with a seat and threadedsections), or combinations of any thereof. The section of the chamberwall that is removably-resealable may be located in the lower portion ofthe chamber. Alternatively, the section that is removably-resealable maybe located in the upper portion of the chamber. Where the chamber is inthe form of a VRC, or substantially in the form of a VRC, theremovably-resealable section may constitute all or part of the planarupper surface of the cylinder. In an embodiment, theremovably-resealable section comprises the upper planar surface of theVRC and a seal at or proximate to its circumference that engages all orpart of the cylindrical wall of the cylinder. In such an embodiment thevertical wall of the VRC may comprise one or more ridges to retain theremovably-sealable upper section and/or a seal or a sealing surface thatengages the upper portion.

The interior volume of a chamber may be varied over a substantial range,for example from about 1 to about 25 liters (e.g., from about 1 to about4, from about 1 to about 8, from about 9 to about 16, from about 12 toabout 25, from about 16 to about 20, from about 18 to about 25, or fromabout 20 to about 25).

VRC chamber and Equilibration Approximate Approximate Ratio ofSpheroidal Chamber Approximate Member Equilibration the Chamber VolumeEquilibrator Diameter Chamber Diameter Member to EquilibrationCombination (cm) Volume (cm³) (cm) Volume (cm³) Member Volume #1  11-12 950-1360 10  524 1.8-2.9 #2  13-14 1600-2440 12  904 1.8-2.9 #3  15-162600-3900 14  1437 1.8-2.9 #4  17-18 3900-5800 16  2145 1.8-2.9 #5 19-20 5500-8250 18  3053 1.8-2.9 #6  21-22  7500-11300 20  4189 1.8-2.9#7  23-24 10000-15000 22  5575 1.8-2.9 #8  25-26 13000-19550 24  72381.8-2.9 #9  27-28 16550-24850 26  9202 1.8-2.9 #10 29-30 21500-31000 2811494 1.8-2.9 #11 31-32 25450-38200 30 14137 1.8-2.9 #12 33-3430900-46300 32 17157 1.8-2.9

Using a chamber that has a shape that substantially matches thecontoured shape of the equilibration member, the head space can bereduced. For example a spheroidal chamber and spheroidal equilibrationmember combination can have chamber volume : equilibration volume ratiofrom about 3.3 to 2.0 with a equilibration member to head space ratiofrom about 0.3 to 1.0 (head space volume divided by equilibration membervolume) .

3. Positioning of the Equilibration Member and the Location of theInlets and Outlets

The equilibration member may be positioned and held in place within thechamber in a number of different ways, including those that arepermanent (affixing the equilibration member to the interior of thechamber in a non-removable manner), non-permanent (holding theequilibration member in place by contact with the chamber interior orsupports within the chamber interior (e.g., annular supports, pedestals,etc.).

Examples of permanent ways of affixing the equilibration member to theinterior of the chamber include the use of adhesives or fusing theequilibration member to the chamber at one or more points.

Non-permanent methods of positioning and holding the equilibrationmember in place permit the removal of the equilibration member from thechamber for cleaning and/or servicing the apparatus.

In an embodiment the equilibration member is held in place in anon-permanent manner by gravity and is directly removable from thechamber once all or part of a section of the chamber wall that issufficient in size to extract the equilibration member is removed. Amongthe non-permanent structures that may be used to retain theequilibration member in place are studs and/or rings on the interiorsurface of the chamber that position and hold the equilibration memberin place during operation by contacting it. Alternatively, studs and/orrings may be on the surface of the equilibration member and hold themember in place by contacting the interior surface of the chamber.Another alternative is the use of a combination of studs and/or ringsattached to the chamber and equilibration member. The use ofnon-permanent methods of positioning the equilibration member permitsthe equilibration member to be removed (e.g., lifted) out of the camberfor cleaning and maintenance of the member and/or chamber once aremovably-resealable chamber wall section is disengaged and the chamberis opened.

The equilibration member may also be affixed to the chamber usingnon-permanent connections such as screws, clamps, latches, magnets andthe like that can be removed or uncoupled to free the equilibrationmember and permit its removal from the chamber once aremovably-resealable chamber wall section is disengaged and the chamberis opened.

In an embodiment, a cylindrical pedestal is placed vertically beneaththe equilibrium member with the axis of rotation the cylindrical member,the equilibration member, and the central axis of equilibration chamberall substantially aligned. The pedestal, which may be permanently ornon-permanently affixed to the equilibration member, positions theequilibration member properly for generation of falling liquid film andalso serves as an additional falling film surface as liquid transitionsfrom the equilibrium member and flows over the pedestal surface beforedraining out of container. Where the pedestal is solid, or does notreadily permit gas to exchange with any space within the pedestal, thenvolume of the pedestal positioning member also reduces the amount ofheadspace volume inside the equilibrium chamber.

In an embodiment, the equilibration member is positioned within thechamber by a ring, annular projection, or concave section formed in thelower portion of the chamber. In such an embodiment, the equilibrationmember may be made of a magnetically susceptible material or comprise amagnet or magnetically susceptible material, such that the equilibrationmember may be magnetically engaged to the interior surface of thechamber by a magnet located (positioned) on or in the chamber wall. Theequilibration member may also be magnetically engaged in a positionproximate to, but not in direct contact with, the chamber wall (e.g.,the lower portion of the chamber wall) where it is supported by studs oran annular element (ring). Such an embodiment is shown in FIG. 3, wherethe chamber is a VRC and a spherical equilibration member is heldagainst an annular element that is in contact with the substantiallyplanar lower interior surface of the VRC.

In an embodiment the equilibration member is mounted inside a chamberusing a series of stand-off posts alone or in combination with anannular element.

In an embodiment the equilibration member is positioned inside theequilibration chamber by floating on a surface of the liquid (e.g.,water) that accumulates at the bottom of the equilibration chamber priorto draining. In this embodiment, a spherical equilibrium member caneither rotate freely or remain relatively stationary depending on theattack angle and force of the water introduced into the chamber and ontothe member through in inlet port (e.g., the liquid in the chamber actsas a hydrodynamic bearing). In such an embodiment, the equilibrationmember can be kept approximately centered in the chamber by the use ofsmall posts or ribs (e.g., either parallel to or perpendicular to thecentral axis) on the chamber's inside surface.

In an embodiment, the equilibration member may be suspended from theupper portion of the chamber. In one such embodiment, the equilibrationmember is suspended by a flexible material (e.g., a strand of wire,string, plastic, fiber glass, rubber etc.) from the upper portion of thechamber at or near the point where the central axis passes through thechamber wall (e.g., at or near the center of the lid). Equilibrationmembers suspended from the upper portion of the chamber can act like apendulum and have the tendency to stay centered under the liquidentering the chamber from a centrally located liquid inlet when thechamber is tilted.

Equilibration members are generally positioned in the chamber such thatthere is a gap between the equilibration member and the chamber wall.The gap permits a liquid (e.g., water) introduced into the upper part ofthe chamber that runs over the equilibration member to reach the lowerportion of the chamber unimpeded. At the same time, air or a carrier gasintroduced into the lower part of the chamber via the gas inlet canfreely move to the upper portion of the chamber through the gap. The gapis generally distributed uniformly around the equilibration member butthere does not have to be a completely uniform gap and the equilibrationmember may even contact the chamber wall at one or more points. Whilethe size of the gap between the chamber wall and the equilibrationmember may vary, a gap in the range of 0.1 cm to 2.5 cm (0.1-0.5,0.5-1.0, 1.0-1.5, 1.0-2.0, 1.5-2.5, or 2.0-2.5) will generally besufficient to permit passage of the gas and the liquid.

In an embodiment, the chamber is a VRC having an interior volume of fromabout 1.6 liters to 25 liters and a diameter of about 6.5 cm to about 33cm. In such an embodiment, a spherical equilibration member having adiameter that is from about 0.2 cm to about 5 cm (e.g., about 0.2cm-about 1.0 cm, about 0.2 cm-about 2.0 cm, about 2.0 cm-about 4.0 cm,or about 2.5 cm-about 5 cm) less than the inner diameter of the chambermay be employed. Accordingly, where there is a difference in diameter of0.2 cm to 5 cm and the equilibration member's axis of rotation and thecentral axis of the chamber are aligned, there will be a uniform gap offrom about 0.1 cm to about 2.5 cm (e.g., about 0.1 to about 0.5 cm,about 0.5 to about 1.0 cm, about 1.0 to about 2.0, or about 2.0 to about2.5 cm) between the equilibration member and the chamber wall at theequator of the equilibration member or the location of the equilibrationmember with the greatest diameter or radius.

In another embodiment, the chamber is spherical and has a volume of fromabout 1.0-18.0 liters (12.7 cm to about 33.0 cm in diameter), and theequilibration member is spherical and has a diameter that is less thanthe inner diameter of the chamber's interior by about 0.2 cm to about 8cm. Accordingly, when the equilibration member's axis of rotation andthe central axis of the chamber are aligned, there will be a uniform gapof from about 0.1 cm to about 4 cm (e.g., about 0.5-about 1.0 cm, about1.0-about 2.0, or about 2.0-about 4 cm) between the equilibration memberand the chamber wall.

The liquid inlet(s) may be positioned in the upper portion of thechamber such that liquid introduced via the liquid inlet(s) can form afilm over greater than 50%, 60%, 70%, 80%, 90%, or 95% of its surfacearea as the liquid is drawn downward over the equilibration member bygravity. Liquid inlets may include liquid inlet nozzle(s) that directthe stream of incoming liquid at the equilibration member. The liquidstream may be introduced at a relatively slow rate such that gravitywill substantially control the location where the liquid will strike theequilibration member. Alternatively, the liquid may be introduced as astream that can be directed at the equilibration member by the liquidinlet (nozzle). In such embodiments, the liquid stream may be directedsuch that it will impact the surface at an angle that is perpendicularto the surface of the equilibration member at the point of impact.

In an embodiment, the introduction of liquid may be accomplished using asingle liquid inlet (e.g., a liquid inlet nozzle) located at the pointwhere the central axis of the chamber intersects the upper portion ofthe chamber wall. For example, where the chamber is a VRC or a spheroid,a single liquid inlet may be located at the center of the upper planarsurface of the VRC or at the top of the spheroid respectively. The useof a single inlet located where the central axis of the chamberintersects the upper portion of the chamber wall permits theequilibrator to be operated when the central axis of the equilibrator(and the axis of rotation of the equilibration member) are displacedfrom 0° to about 15° or more from the vertical (e.g., the equilibratormay be tilted 0°-10° or)0°-15° without disruption of its operation.

In other embodiments more than one liquid inlet (e.g., nozzle) may belocated in the upper portion of the chamber such that water from one,two, three or more inlets is directed at the surface of theequilibration member. In one embodiment the inlets are spaced around(e.g., equidistant from) the point where the central axis of the chamberintersects the upper section of the chamber surface. Such embodimentsinclude the placement of the liquid inlet at the corners of regularpolygons (e.g., triangle, square, pentagon, hexagon, heptagon, oroctagon) centered at the point where the central axis of the chamberintersects the upper section of the chamber surface. The liquidinlet(s), regardless of how they are arranged, may be placed in aportion of the chamber wall that is removably-resealable or in a portionof the chamber wall that is not removably-resealable with the portion ofthe chamber that retains the equilibration member. For example, wherethe chamber is substantially in the form of a VRC, all or part of thesubstantially planar upper surface of the VRC may act as a “lid” for theremainder of the chamber.

As the equilibrators are of a design that is substantially symmetricallyabout the central axis of the chamber, the equilibrator can be operatedwhen the central axis is displaced from the vertical in any direction.As indicated above, the equilibrators may be operated when the centralaxis is displaced from about 0° to about 15° from the vertical. The useof higher liquid flow rates and/or liquid inlets with nozzles thatdirect liquid at the equilibration member increases the angle at whichthe equilibrator may be operated. In one embodiment the nozzles mayextend into the chamber terminating proximate to the equilibrationmember such that they direct the incoming liquid at the equilibrationmember at an angle that is substantially normal to surface at the pointwhere the liquid stream contacts the equilibration member. In someembodiments the equilibrator may be operated when the central axis isdisplaced (the equilibrator is tipped) up to about 20°, 25° or 30° fromthe vertical. The ability of the equilibrator to operate when tippedpermits its use on, for example, floating platforms where waves may rockthe equilibrator.

Liquid inlets and tubing bringing liquids to the inlets will typicallyhave an inner diameter greater than 2 mm, for example in the range ofabout 2.0 to about 14.0 mm (e.g., 2.0-4.0, 2.0-6.0, 4.0-8.0, 6.0-10.0,8.0-14.0. or 10-14 mm). Liquid inlets may terminate at or be in the formof a nozzle that extends into the chamber to direct the stream ofincoming liquid at the equilibration member. Nozzles, when present, willbe in the same size range as the tubing bringing liquid to the inlets,namely about 2.0 to about 14.0 mm (e.g., 2.0-4.0, 2.0-6.0, 4.0-8.0,6.0-10.0, 8.0-14.0. or 10-14 mm). In an embodiment where the chamber isin the form of a VRC, the liquid inlets are placed on the substantiallyplanar upper portion of the chamber and may be distributed as describedabove-with regard to the central axis.

One or more liquid outlets are located in the lower portion of thechamber and positioned to permit outflow of some or all of the liquidthat collects in the lower portion of the chamber by gravity. Where thechamber is in the form of a VRC, the liquid outlet(s) may be in thecylindrical side wall of the chamber and/or in the substantially planarlower surface of the chamber. Where the chamber is spheroidal, ovoidal,or ellipsoidal, a single liquid outlet may be located at the point wherethe central axis of the chamber intersects the lower portion of theequilibrator chamber. In an embodiment, the chamber has the overallshape of a VRC, with the lower surface of the chamber modified either toa convex shape and/or to accommodate channels that direct liquids thatare drawn to the bottom of the chamber by gravity toward one or moreliquid outlets in the convex surface and/or in the channels.

Liquid inlets and the tubing carrying liquid away from the outlet willtypically have an inner diameter of a similar size to the liquid inlet;however, where the liquid inlet is typically under pump pressure and theoutlet passively drains liquid under the force of gravity, the diametersmay deviate somewhat. More specifically, the liquid outlet willgenerally have an inner diameter greater than 2 mm, for example in therange of about 2.0 to about 20.0 mm (e.g., 2.0-4.0, 2.0-6.0, 4.0-8.0,6.0-10.0, 8.0-14.0, 10-14, or 14-20 mm). During operation of theequilibrator the liquid outlet should not permit air to enter thechamber by allowing liquid to drain away too quickly, and at the sametime liquid should not flood/overfill the chamber. Accordingly, theliquid outlet may be sized to maintain at least some liquid in the lowerportion of the chamber. The cross sectional area of the liquid outlet,or a portion of the tubing attached to it may be adjustable and set toaccommodate specific liquid out-flow rates by use of a valve or clampthat compresses/constricts the liquid outlet and/or the tubing attachedto the outlet. Alternatively, a U-shaped liquid trap, a valve, a one-wayflow valve (e.g., a check valve, flapper valve or feather valve)installed in the tubing that carrying liquid away from the equilibratormay be utilized to prevent air from entering the chamber through theliquid outlet.

Regardless of the shape of the chamber, placement of at least one of theone or more liquid outlets at or near the lowest point of the chamber(as determined when the central axis of the chamber is vertical) permitsthe clearance of solid/semisolid materials (e.g., sediment) from thechamber, which extends the time between cleanings necessary to maintainproper operation (gas equilibration). Where the equilibration member ispositioned in the chamber by a ring, annular projection, or concavesection formed in the lower portion of the chamber, any of thoseelements may be provided with channels, grooves or gaps so that liquidcan reach the liquid outlet. The ring or annular projection may be ofany suitable dimension. In an embodiment the ring will be formed from ahoop of a material (e.g., tubing) having a circular cross-section with adiameter of about 8 to 30 mm. Annular projections built into the wall ofthe chamber may be of similar size and shape to rings used to supportthe equilibration member (e.g. 0.7 to 2 cm in diameter/height). As withrings, annular projections built into the chamber wall used to supportthe equilibration member are provided with gaps or openings to permitthe flow of liquids to and from the space below the equilibration memberas needed, for example where the liquid outlet may be located. Theequilibration chamber may be provided with external supports (e.g.,external legs or a pedestal) to provide stability when placed on ahorizontal surface and/or where the liquid outlet is located low enoughon the chamber (e.g., on the bottom of a VRC chamber) that it wouldinterfere with stable placement of the apparatus on a horizontal supportsurface.

One or more gas inlets are located in the wall of the lower portion ofthe chamber. Gas inlets are generally placed in the wall of the lowerportion of the chamber at a point above the level of the liquidoutlet(s). Placement in that manner is, however, not required providedthat any mechanism used to introduce gas into the chamber providessufficient pressure to prevent liquid in the chamber from backing upinto the gas inlet(s) or the tube(s) supplying gas to the gas inlet(s).

Accordingly, in an embodiment, the gas inlet(s) may be place in the wallof the lower portion of the chamber at a point above the level of theliquid outlet(s) as determined when the central axis of the chamber isvertical. In another embodiment, the gas inlet(s) may be placed in thewall of the lower portion of the chamber above the level at which liquidcan accumulate in the chamber as determined when the central axis of thechamber is 10°, 12°, 15°, 20°, 25° or 30° from the vertical, taking intoconsideration the location of the liquid outlet(s). In other embodimentsthe gas inlets are placed in the wall of the lower portion of thechamber at or below the level of the liquid outlet(s) as determined whenthe central axis of the chamber is vertical. In such an embodiment gasentering the chamber will bubble through the liquid as it enters.

Gas inlet(s) may terminate in a nozzle that diffuses the gas as itenters the chamber, or directs the gas entering the chamber in aspecific direction. A combination of nozzles that diffuse gas or directit in one or more directions may be employed. In an embodiment, wheregas enters the chamber in a diffuse undirected fashion, it will causeturbulence in the gas in the lower portion of the chamber that mayassist in the equilibration of the gases present in the liquid with thegas phase. In another embodiment, nozzles may direct a stream of gasentering the chamber toward the central axis of the chamber. In otherembodiments, nozzles may direct gas entering the chamber away from thecentral axis of the chamber. For example, nozzles may direct gasentering the chamber along the interior surface of the chamber (parallelto the wall) at the point where the nozzle is located, thereby directingthe gas in the lower portion of the chamber to circulate around thecentral axis.

One or more gas outlet(s) are located in the upper portion of thechamber's wall, and may be provided with a shield to prevent droplets ofliquid that splash in their direction from entering the gas outlet (seeFIGS. 7A and 7B). The gas outlets are positioned to avoid the intake ofliquid, and accordingly, may be located in the chamber wall above thelevel of the liquid inlet(s). Where the liquid inlet(s) comprise anozzle the extends into the chamber, the gas outlets may be locatedabove the level where the liquid is discharged from the nozzle. Wherethe chamber is in, or substantially in, the form of a VRC, the gasoutlets may be positioned on the substantially planar upper surfacealong with the liquid inlet(s). In an embodiment, the gas inlet(s) arelocated in a portion of the chamber wall that is removably-resealablewith the portion of the chamber that retains the equilibration member.In such an embodiment, the removably-resealable portion of the chamberwall with the gas outlets may also contain one or more of the liquidinlets. Gas outlets also may be located in the upper portion of thechamber's wall that is not removably-resealable. In an embodiment, wherethe chamber is substantially in the form of a VRC, one or more of theliquid inlets and/or one or more of the gas outlets may be located inthe substantially planar upper surface of the VRC, which acts as a “lid”for the remainder of the chamber.

The inner diameter of the gas inlets, and of the tubing connecting them,may be of any suitable size to accommodate the flow of gas to and fromthe chamber. In an embodiment, the inner diameter of gas inlets andoutlets, and of the tubing connected to them, will be up to about 8 mm(e.g., up to about 6 mm or in the range of 4-8 mm) outside diameter witha wall thickness of about 0.5 mm or less giving an inside diameter up toabout 7 mm (e.g. from about 3mm to 7mm) inside diameter . In otherembodiments, the gas inlet(s), the gas outlet(s) and the tubingconnected to them, each have an inner diameter selected independentlyfrom a range selected from: 1-12.5, 1-2, 2-4, 2-6, 2-8, 4-6, 4-8,4-12.5, 6-10, 6-12.5 and 8-12.5 mm.

4. Materials for Chamber and Equilibration Member

The equilibrator apparatus may be constructed of any suitable materials.Generally, the materials used for construction, particularly of theequilibration member, are not porous and do not absorb water, as trappedwater could interfere with gas exchange and/or increase the timerequired for the gas stream passing through the equilibrator to reflectthe concentration of gases in the liquid being sampled (increase theresponse time of the equilibrator).

Generally the equilibrator components are constructed of a plastic(e.g., thermoset or thermoformed polymer) and/or metal that is selectedindependently for each component of the equilibrator. Such plasticsinclude, but are not limited to, acrylonitrile butadiene styrene (ABS),acrylics (e.g., polymethyl methylacrylate), epoxy, polyamide (e.g.,nylons), polycarbonate, polyester, polyether ether ketone (PEEK),polyetherketoneketone (PEKK), polyethylene (e.g., low density or highdensity polyethylene), polyethylene terephthalate, polypropylene,polystyrene, polysulfone, polyphenylsulfone, polytetrafluoroethylene(e.g., Teflon), polyvinyl chloride (PVC), polyurethane, ureaformaldehyde, vinyl and combinations thereof. Metals that may beemployed include, but are not limited to, aluminum, iron, steel,stainless steel, titanium, zinc, brass, or bronze and combinationsthereof. Metal components may be coated with a polymer coating, anenamel coating, a sacrificial metal coating (e.g., zinc galvanizing), ora barrier metal coating (e.g. chrome) to avoid corrosion.

In an embodiment the chamber is formed from polypropylene and/orpolyethylene and the equilibration member is formed from polypropyleneand/or polyethylene or a metal such as steel that is coated to avoidcorrosion. In such an embodiment, magnetic materials may be incorporatedinto the equilibration member to make it susceptible to magneticlocalization inside of the chamber as discussed above.

Seals, which may be used, for example, in conjunction withremovably-sealable portions of the chamber wall, and with gas and liquidinlets and/or outlets, can be formed from a variety of suitablematerials. Materials suitable for forming seals include, but are notlimited to, natural or synthetic rubbers (e.g., silicone rubber).

Long periods of exposure to daylight can negatively impact theequilibrator. Where plastics and/or rubbers or other materials that aresusceptible to photo degradation/damage are used, they may include lightstabilizers including, but not limited to, antioxidants, hindered aminelight stabilizers, UV absorbers and the like. In addition, exposure tolight permits the growth of algae and other organism, particularly whenthe liquid being tested is an aqueous liquid (e.g., fresh water, seawater and the like). Accordingly, plastics that are colored or containfillers that substantially block or reflect light capable of supportingphotosynthesis (e.g., from about 350 nm to about 750 nm) reduce thepossible fouling of the equipment while extending the period betweenrequired service to keep the equilibrator clean and functioningproperly. Coatings on the exterior of the chamber that reflect or absorblight can be used in place of colored plastics. Additionally, opaquefabric covers or shrouds can be used to protect equilibrator fromharmful or photosynthesis promoting solar radiation.

Where water or other aqueous liquids are subject to measurement, thechamber may be made of materials that are hydrophobic and/or omniphobic,or coated with hydrophobic and/or omniphobic coatings, on all or part ofthe chamber's inner surface (all or part of the outer surface of thechamber may also be coated). Where non-aqueous liquids, or aqueousliquids having substantial amounts of other materials such as alcoholspresent, are subjected to measurement, omniphobic materials and/oromniphobic coatings may be utilized on all or part of the interiorsurface of the chamber (all or part of the outer surface of the chambermay also be coated). By controlling the hydrophobicity or omniphobicityof the chamber's inner surface (or the slide angle with, for example,aqueous test liquids), the response time of the equilibrator may beimproved as droplets of liquid will not stick to the chamber walls, butwill pass through the equilibrator. Another advantage of using a chamberwith a hydrophobic or superhydrophobic inner surface is that suchsurfaces are considered “self-cleaning” as they resist the adherence ofdirt and other materials/organisms that can foul the surface.Accordingly, the use of hydrophobic, superhydrophobic, or omniphobicsurfaces extends the period of equilibrator operation betweenmaintenance required to keep it functioning properly (indicated bymaintaining the e-folding time to within 5%, 10%, 15% or 20% of theinitial e-folding time established with an unfouled (clean) equilibratoroperated under the same conditions (e.g., the equilibrator's initiale-folding time value or the e-folding time value after cleaning).Self-cleaning effects are most pronounced when the surfaces areomniphobic.

In contrast to the chamber's inside walls, where aqueous (or polar)liquids are being tested the equilibration member can be madehydrophilic, thereby encouraging the film of aqueous (or polar) liquidto spread over the equilibration member's surface increasing the surfacearea of the film and the exchange of gases.

In one embodiment, at least the interior surface of the chamber wall ismade hydrophobic (or is made to have a low slide angle with water) andthe equilibration member is made to have a hydrophilic surface. Inanother embodiment, at least the interior surface of the chamber wall ismade superhydrophobic (or is made to have a slide angle with water lessthan) 5° and the equilibration member is made to have a hydrophilicsurface. In another embodiment, at least the interior surface of thechamber wall is made omniphobic and the equilibration member is made tohave a hydrophilic surface.

In an embodiment, all or part of the interior surface of the chamber(e.g. the interior chamber wall that can contact an aqueous test liquid)is hydrophobic and has a contact angle with water greater than about 90°(e.g., greater than about 100°, 110°, 120°, 130°, 140°, 150° or) 160°)at 22° C.

In an embodiment, the interior surface of the chamber (e.g. the interiorchamber wall that can contact an aqueous test liquid) has a slide anglewith water of less than about 30° (e.g., less than about 20°, 10°, or)5°from the horizontal (level) at 22° C. For the purpose of this disclosurethe slide angle for a material is the angle at which half of a set often water droplets, 25 microliters in volume, slide off or to the edgeof a planar piece of the material as its incline is gradually increasedfrom the horizontal (0°). For the purposes of this disclosure, a lowslide angle is less than 10°.

Where the interior of the chamber is not already hydrophobic (e.g.,constructed of a material with a suitable hydrophobicity), the surfaceof the equilibration member may be made hydrophobic or superhydrophobicby chemical treatment or by coating it with a hydrophobic coating. Inone embodiment, all or part of the surface of the chamber (e.g., all orpart of the inner surface of the chamber wall) is modified by treatmentwith hydrophobic silanizing agents (e.g., alkyl and fluoro alkylsilanizing agents). Hydrophobic silanizing agents include, but are notlimited to: (tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosilane;(tridecafluoro-1,1,2,2-tetrahydrooctyl) triethoxysilane;(tridecafluoro-1,1,2,2-tetrahydrooctyl) trimethoxysilane;(heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethyl(dimethylamino)silane;n-octadecyl-trimethoxysilane; n-octyltriethoxysilane; andnonafluorohexyldimethyhl(dimethylamino)silane. In other embodiments, allor par(of the interior surface of the chamber may be treated with ahydrophobic coating to render the treated surfaces hydrophobic orsuperhydrophobic. Hydrophobic coatings include those with polyurethane,acrylic, and fluorovinyl (see, e.g., U.S. Pat. Nos. 5,962,620 and9,067,821) polymer systems. Where it is desirable to have omniphobicbehavior, the silanizing agents and/or coatings (e.g., the polymers ofthe coatings) should comprise fluoroalkyl groups.

In an embodiment, where the liquid subject to testing is an aqueousliquid, the surface of the equilibration member may be made hydrophilic.In such an embodiment, the contact angle of the equilibration memberwith water may be less than about 60° (e.g., less than about 50°, 40°,30°, 20° or)10° at 22° C. As discussed above, contact angles aremeasured using a goniometer.

If the equilibration member is not already hydrophilic (e.g.,constructed of a material with a suitable hydrophilicity), the surfaceof the equilibration member may be made hydrophilic by chemicaltreatment or by coating it with a hydrophilic coating. In oneembodiment, the hydrophilicity of the equilibration member is modifiedby treatment with hydrophilic silanizing agents. Hydrophilic silanizingagents include cyanomethyl, aminopropyl, and glycidoxypropyl silanes(e.g., cyanoethyltrimethoxysilane, aminopropyltriethoxysilane, andglycidoxypropyltriimethoxysilane). In another embodiment the surface ofthe equilibration member (e.g., rubber or plastic) may be treated with aplasma (e.g., oxygen plasma) to provide hydroxyl, carboxyl and carbonylgroups. In other embodiments oxygen plasma treated surfaces aresubsequently treated with a nitrogen plasma to affix nitrogen containinggroups to the surface and render it more hydrophilic. In otherembodiments, all or part of the interior surface of the chamber may betreated with a hydrophilic coating (e.g., hydrophilic polyurethane,acrylic, or hydrogel compositions etc.) to render the treated surfaceshydrophilic (see, e.g., U.S. Pat. Nos. 5,962,620 or 6,017,577 describinghydrogels).

For the purpose of this disclosure, materials or surfaces are consideredto be hydrophobic when the static contact angle of the surface withwater at 22° C. is 90° or greater. Surfaces are considered to besuperhydrophobic when the static contact angle with water at 22° C. isgreater than 150° . Surfaces are considered omniphobic when they have astatic contact angle with both water and hexadecane greater than 90° at22° C. For the purpose of this disclosure, materials or surfaces areconsidered to be hydrophilic when the static contact angle of thesurface with water at 22° C. is less than 90° . Contact angles aremeasured using a goniometer (e.g., Attension Model Theta goniometer,formerly KSV Instruments, available from BIOLIN SCIENTIFIC, Stockholm,Sweden according to the manufacturer's instructions.

5. Operation of the Equilibrator

In general terms, the equilibrator operates by having liquid introducedin the upper portion of the equilibrator chamber such that it contactsthe equilibration member forming a film that is drawn downwards over theequilibration member (a falling film) to the lower portion of thechamber where it is directed to a liquid outlet and leaves theequilibrator. At the same time liquid is introduced into the upperportion of the equilibrator, a carrier gas is introduced into the lowerportion of the chamber. Once introduced into the lower portion of thechamber, the incoming gas is displaced upward by the stream of incomingcarrier gas. As carrier gas moves upward it contacts the falling film ofliquid and the gases (e.g., carbon dioxide) in the liquid exchange intothe carrier gas progressing toward equilibrium concentration as theliquid and carrier gas move in a counter current manner. The carriergas, which is near or has reached equilibration with the gases in theincoming liquid, ultimately reaches the upper portion of the chamberwhere it exits the chamber via the gas outlet(s). After exiting thechamber via the gas outlet(s), all or part of the carrier gas isdirected to the sensor of an analytical instrument (gas analyzer) thatcan measure the amount of the gas of interest in the carrier gas. Wherethe liquid is water or an aqueous solution, systems that incorporate theequilibrator with an analytical instrument may also have adryer/dehumidifier interposed between the gas outlet(s) of theequilibrator and the sensor to remove from the carrier any gas liquidthat condenses in the gas outlet line (sample gas line 8 connected togas outlet 4) and/or any liquid (e.g., water) vapor before the carriergas reaches the sensor 16 of the analytical instrument 17. Equilibratedsample gas(es) are pulled (slight vacuum) through the gas outlet linethrough the dryer/dehumidifier, and into/through the gas sensor by theintake side of a gas/air pump (e.g., a vane, fan, diaphragm etc.) 23that is located downstream from the sensor. Carrier gas is directed fromthe pump outlet under positive pressure into the gas inlet line leadingto the equilibrator. The dryer/dehumidifier will generally be placed“upstream” of the sensor of the gas analyzer when the system isoperating in the forward direction (forward flow of causes carrier gasto move in the direction from the equilibrator's gas outlet toward theanalytical instrument's sensor, reverse flow takes gas in the oppositedirection toward the equilibrators gas outlet). The dryer/dehumidifier 9may comprise one or more of a water trap 10, a filter 11 (e.g., amembrane filter made of paper, nylon, polyvinylidene difluoride (PVDF)and the like), and/or drying tube assembly 12. The drying tube assemblymay comprise a dehumidifying Nafion© polymer tube 13 that is suppliedwith a flow of drying gas (e.g., air) through a drying gas inlet 14 anddrying gas outlet 15 that has a lower amount of the water vapor suchthat it can dehumidify/dry the carrier gas stream coming from theequilibrator.

In an embodiment, carrier gas (e.g., air or an inert gas) exiting thechamber via the gas outlet(s), along with the gas of interest and liquidvapor (e.g., water vapor), is recirculated back to the gas inlet(s)after passing through one or more sensor of the analytical instrument 16and the dryer/dehumidifier 9 if present. The gas may thus be kept in aclosed loop except during periods when all or part of it is replaced ordisplaced by fresh carrier gas or when a gas standard is used tocalibrate the analytical instrument. Analytical instrument 17 maycontain a single type of sensor (e.g., CO₂) or multiple sensors arrangedin parallel and/or in series that detect different species within thecarrier gas stream (e.g., CO₂, methane, radon etc.). Accordingly,different species can be detected using the same equilibrated samplegas, either by placing sensors in series within a single gas train or inparallel where the gas train has been split after leaving theequilibrator and rejoined prior to entering the equilibrator gas inlet.In an embodiment, the analytical instrument contains at least a firstsensor that is in arranged in parallel with a second sensor, and a thirdsensor in series with the first sensor.

Where the liquid subject to analysis is forms as condensate (e.g.,aqueous solutions or water), it may be desirable to periodically reversethe flow of gas in the line (tubing) attached to the gas outlet so thatliquid that has been swept into and/or condensed in the lines is carriedback into the chamber and to remove liquid from the dryer/dehumidifier9. In some embodiments, the gas flow may be reversed through a segmentof the line proximate to the gas outlet of the chamber 8 passing throughthe dryer/dehumidifier 9 (if present) and exhausted at port 19 or afterpassing through the chamber at port 22 (from sampling port 20 which isexhausted at port 19 or 22). In other embodiments, the flow may bereversed through both the dryer humidifier 9 and the sensor 16 (e.g.,gas low from sample port 21 which is exhausted at port 19 or 22). Valves19 a, 20 a, 21 a, and 22 a are capable of connecting and closing off anycombination of lines connected to them, but when measurements of a gasof interest in a liquid sample are being made they close off only theline to ports 19, 20, 21, and 22. Where gas circulation is reversedthrough the chamber it can be advantageous to stop the flow of liquidinto the chamber during the period of reverse flow using a valve 18upstream of liquid inlet 1.

Where gas flow is reversed for the purpose of clearing the gas lines ofcondensed liquids and/or drying the gas lines, previously unused carriergas or gas used for standardization/calibration of the equipment (e.g.,air or a gas with a known CO₂ or other gas species concentration) may bedirected into the system (e.g., via a port 20 or 21) at one end of thesection of the equipment to be dried and/or calibrated, and allowed toexit at a point downstream of the portion subject to drying and/orcalibration.

In view of the foregoing, in one embodiment, an apparatus comprising anequilibrator as described herein may be operated to determine the amountof one or more gases of interest present in a liquid employing a methodcomprising the steps:

-   -   i) providing an apparatus of any one of embodiments 1-25        (enumerated below);    -   ii) introducing the liquid into the chamber of the apparatus by        way of the liquid inlet such that it passes over the        equilibration member and exits the apparatus by way of the        liquid outlet;    -   iii) directing a carrier gas into the apparatus by way of the        gas inlet such that it flows over the equilibration member in a        direction that is counter current to the flow of the liquid and        exits the chamber of the apparatus by way of the gas outlet;    -   iv) directing all or part of the gas that exits the chamber to a        sensor of an analytical instrument that determines the amount of        the gas or gases of interest present in the liquid; and    -   v) determining the amount of a gas or gases of interest present        in the liquid based on the output of the detection system.

In some embodiments, in addition to the equilibrator, the sensor of theanalytical instrument, and an optional dryer/dehumidifier, the systemmay comprise an auto-controlled drying mechanism and carrier gas (e.g.,atmospheric gas/air) sampling port circuit composed of a combination ofsolenoid and valves (e.g., one-way valves) and an electrical relay tosimultaneously stop water pumping into the equilibrator. In suchembodiments, the method may further comprise the steps of samplingcarrier gas (e.g., air from the atmosphere) through the carrier gassampling port (by opening a valve to that port) and directing it to thesensor for measurement/calibration purposes, after which it is exhaustedtoward the equilibrator through the same sample gas line that connectsthe gas out of the equilibrator chamber to the sensor system. By doingso, the line that normally brings gas laden with liquid vapor (e.g.,water vapor) from the equilibrator to the sensor system can be clearedof accumulated liquid that has, for example, condensed in the line andthe sensor system. By directing carrier gas from the sampling port thatis not saturated with liquid vapor (e.g., water vapor) through thedryer/dehumidifier, the dryer/dehumidifier apparatus and/or any chemicaldrying agents it contains may be fully or partially regenerated.Alternatively, the chemical drying agent may be contained in a chamberequipped with a heating element and may be periodically regenerated byheating the drying agent if the apparatus is located where energyconsumption of the drying process can be provided. In an embodiment,samples of the chemical drying agent are replaced periodically at timesdetermined by the climate/ambient relative humidity and temperatureinstead of being regenerated.

The frequency with which the flow of gas is reversed to remove all orpart of the liquid that might accumulate in the lines (tubing) carryinggas from the equilibrator the sensor system can vary depending on avariety of factors. Fluid accumulation in the line leading from the gasoutlet of the chamber to the sensor is often the result of condensationof vapor from the fluid being sampled becoming part of the carrier gasstream. Accordingly, the temperature of the fluid, which will change itsvapor pressure, and the temperature of the line, which is largelydictated by ambient temperature of the location where the sensor part ofthe system is installed, may in large part dictate the need for clearingthe line of fluid. In embodiments, the direction of gas flow is reversedto clear the lines during less than 25% (e.g., less than 20, 15, 10 or5%) of its operating time. By way of example, a system encompassing theequilibrator may have the direction of gas flow reversed for acontinuous period of 15 minutes every one, two, three, four, five, orsix hours. Under field conditions, 15 minutes per six hours operatingtime is often sufficient and provides the opportunity to measure ambientatmospheric gas concentrations (e.g., ambient pCO₂ values).

As discussed above, the equilibrator functions by permitting theexchange of the gas of interest between the film of fluid being drawndownward over the equilibration member (falling film) and the gas movingup through the equilibrator. Accordingly, efficient exchange requiresthe film of liquid have sufficient area. At the same time, the gas flowshould be sufficient to provide a suitable response time, but not sofast as to cause turbulence in the equilibrator (e.g., turbulence thatcarries water droplets into the gas outlet(s)). The flow of liquid intothe equilibrator required to provide a film of sufficient area dependson many factors including, but not limited to, the shape of theequilibration member, its dimensions (including surface area), theviscosity of the liquid, and the interaction between the liquid and thesurface (e.g., is there enough interaction energy between the surfaceand the liquid for efficient wetting). In general, falling films areinitiated with liquid of sufficient volume that is injected with somepositive pressure onto the top surface of the equilibration member tocompletely wet the surface of the equilibration member and to maximizethe integrated wetted surface area over time. Larger equilibrationmembers will have more instantaneous wetted surface area than smallerequilibration members.

In an embodiment, the flow of liquid required to maintain a falling filmover the surface of the equilibration member may vary from about 0.25liters/minute (l/min) to about 12 l/min (e.g., 0.25-1, 0.25-2, 1-4, 2-6,4-8, 6-12 or 8-12). Exact flow rates will be limited by the equilibratormember surface area and drain diameter, and thus may have potential forbroad working range. Lower flow rates, such as 0.25 or 1.0 l/min, areuseful with smaller equilibration members (e.g., those with surfaceareas of less than 1000 cm²) and higher flow rates, such as 6-12 or 8-12l/min, with larger equilibration members (e.g., those with surface areasof 1000 cm² or greater).

Gas flow rates through the chamber during operation necessary to obtainmeasurements will vary depending on a variety of factors including, butnot limited to, the interior volume of the chamber, the shape of thechamber, and the desired response time of the apparatus to changes inthe content of a gas of interest in the liquid being sampled. In anembodiment, the gas flow may vary from about 0.25 liters/minute (l/min)to about 3 l/min (e.g., 0.1-1, 1-2, or 2-3 l/min). Flow rates (e.g., incm³/min.) may be adjusted based on the chamber's headspace (interiorvolume not occupied by the equilibration member or support structuressuch as annular rings and/or pedestals), with lower flow rates of about0.08 to about 2.5 cm³ of carrier gas per cm³ of headspace per min.(e.g., from about 0.08 to about 0.2, about 0.2 to about 0.5, about 0.5to about 1.0, about 1.0 to about 2.0, or from about 2.0 to 2.5 cm³ ofcarrier gas/(cm³ of headspace) per minute).

For operation the equilibrator apparatus described herein can be mountedto a stationary mount. Alternatively, because the equilibrator canoperate when tipped at moderate angles, it can be mounted on a mobileplatform such as a boat, buoy, raft or similar platform permitting arange of installation options for measuring gases of interest. Theequilibrator is not disturbed by bubbles or particulates small enough topass through the lines/nozzles used to deliver liquids to the chamberand/or the fluid outlet and lines that carry liquid away from theequilibrator's chamber.

Because various gas species are produced through both natural andengineered processes, measurements of gas concentration is important forunderstanding many aspects of water quality. There are many applicationsfor equilibration and measurement that address both environmental andhuman health issues. Virtually any gas species that can be absorbed inwater (natural surface waters, pore water, groundwater/aquifer, or waterwithin engineered water systems such as well water, waste watertreatment facilities, drinking water treatment plants, swimming pools,algal photobioreactor systems used for carbon capture and sequestration,etc.) can be equilibrated or substantially equilibrated with carrier gasor air in the headspace (the chamber's interior volume not occupied bythe equilibration member and any supports, such as pedestals or annularrings, used to support the equilibration member) of the falling filmequilibrators described herein regardless of the relative solubility ofthe gas. Gas species can then be measured by use of the appropriateanalytical instrument and sensor (e.g., NDIR, photo-acoustic detectors,gas chromatographs, radiation such as alpha particles) in either realtime or as discrete samples.

Among the gases that could be measured using the falling filmequilibrators described herein are ammonia, CO₂, CO, sulfur oxides(e.g., sulfur dioxide), nitrogen oxides (e.g., NO or NO₂), methane,ethane, hydrocarbons, halogenated hydrocarbons, chlorofluorocarbons(CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), esters,sulfur hexafluoride (SF₆), chlorine, bromine, radon, hydrogen sulfide(H₂S), HF, HCl, HBr, and HI. Measurements can be made, for example, ofone, two, three or more of such gases. By way of example, measurement ofCO₂ can be made by infrared detection and measurement of radon by usinga detector for alpha-radiation. Some gases/volatile materialsparticularly relevant to human health and/or of environmental concernthat can be measured in, for example, aqueous samples using the fallingfilm equilibrator described herein include carbon dioxide, methane,radon, hydrogen sulfide, halogenated alkanes (e.g., trihalomethanes),sulfur hexafluoride, nitrous oxide, and sulfur dioxide.

Carbon dioxide (CO₂) can be measured to determine its concentration asrelated to carbonate chemistry (the chemistry of ocean acidificationcomprised of total dissolved inorganic carbon, carbonate, bicarbonate,pH, total alkalinity, etc.), CO₂ sources/sinks (e.g., estuaries, rivers,streams), pCO₂/pH control (e.g., monitoring and control of pH inswimming pools), ecosystem metabolism (e.g., photosynthesis/respirationpatterns), and carbon capture/sequestration in industrial settings, andin understanding greenhouse gas effects.

Methane (CH₄) is an important gas to monitor as it is both a greenhousegas with 25× forcing potential than CO₂ and explosive if it builds up tosignificant levels. Methane can occur in drinking water, waste water,groundwater/aquifers, pore water in natural aquatic systems (e.g.,lakes, rivers, streams, wetlands), in engineered environments such asindustrial ponds, and in water released from industrial processes andengineered environments. Sources of methane include industrial (e.g.,petroleum) processing, natural gas release, and agricultural sources(livestock and manure).

Radon (Rn) is a human health hazard linked to the development of lungcancer produced naturally via the radioactive decay of uranium inbedrock and occurs in well water, aquifers, rivers, the sump of numeroushomes, etc.

Hydrogen sulfide (H₂S), is a poisonous, corrosive, flammable gasproduced by anaerobic microbial decomposition of organic materials inwetlands and sewers, and also occurs in natural gas and volcanic gases.

Halogenated alkanes, including total trihalomethanes (e.g., chloroform(CHCl₃), bromoform (CHBr₃), dibromochloromethane (CHBr₂Cl), andbromodichloromethane (CHBrCl₂), are a human health hazard due to theirtoxicity. Trihalomethanes are common water disinfection byproductsresulting from water chlorination. While the concentration ofhalogenated alkanes is regulated in drinking water, they occur commonlyin swimming pools.

Sulfur hexafluoride (SF₆), which is used as a tracer gas and anelectrical insulator, represents a substantial environmental hazard.Sulfur hexafluoride is one of, if not the, most potent greenhouse gas,as evaluated by PICCC (Primary Industries Climate Challenges Centre)having 22,000× forcing potential of CO₂.

Nitrous oxide (N₂O) is an environmentally hazardous material that cancontribute to greenhouse warming (298× forcing potential of CO₂).Nitrous oxide is produced naturally by microbial processes in soils,manure, and the ocean. The gas also results from anthropogenic sourcessuch as fertilized soils. It is used extensively as an aerosolpropellant, in medical and dental procedures as an anesthetic, and as asupplementary oxidizer for internal combustion engines and in rocketfuel.

Sulfur dioxide (SO₂) is a major air pollutant that impacts human health.It is a precursor to inorganic acids and a component of acid rain.Sulfur dioxide has its environmental origins in volcanic sources and inthe industrial combustion of sulfur containing materials.

A large variety of liquids can be assessed for the levels of dissolvedgases and/or volatile components including salt water, sea water,brackish water, tidal water, marsh water, river water, lake water,stream water, spring water, ground water, aquifer water, pore water,geyser water, volcanic water, well water, swimming pool water, aquariumwater, sewage (e.g., sewer water), industrial waste streams, industrialwaste water, irrigation water, run-off from agricultural sites, run-offfrom mines, run-off from industrial sites, drinking water, treatmentplant water, and treated sewer water.

The design of the equilibrator permits monitoring of one or more gasspecies in a continuous or semi-continuous fashion (continuous, exceptduring intervals where the equilibrator is operated with gas flow in thereverse direction to clear liquid) as opposed to taking discrete sampleswhich are subject to analysis. It is also possible to incorporateadditional sensors into the equilibrator or the adjacent analyticalequipment to measure the characteristics of the fluid being measuredsuch as temperature and pH, which can be measured in the body of liquidsubject to testing, in the chamber, or in the lines (tubing) connectedto the equilibrator.

Operation of the equilibrator and the system it is connected to for theanalysis of gases of interest in liquid samples requires controlling theflow of both liquids and gases. Liquids may be direct to flow by the useof any suitable pump including, but not limited to, vane, impeller,piston, centrifuge and diaphragm pumps, any or all of which may bereversible. Similarly, the flow of gases may be directed by the use ofpumps including, but not limited to, vane, impeller, piston, centrifuge,bellows and diaphragm pumps, any or all of which may be reversible.Gases may also be directed to flow by use of a source of previouslycompressed gas (e.g., a pressurized tank) or by the application ofreduced pressure (vacuum or partial vacuum). In operation, the movementof gases may be directed in a system incorporating an equilibrator usingany combination of pumps, vacuum and compressed gas sources.

Certain Embodiments

-   1. An apparatus comprising:    -   a chamber comprising an outer wall that is disposed        substantially symmetrically about a central axis, the outer wall        defining the interior surface of the chamber, the exterior        surface of the chamber, and space within the chamber;    -   an equilibration member within the chamber having an        equilibration member surface, an axis of rotation, and a        bisecting plane perpendicular to the axis of rotation positioned        at the midpoint of the equilibration member's axis of rotation;    -   the equilibration member being positioned within the chamber        such that its axis of rotation and the central axis of the        chamber coincide or substantially coincide;    -   the chamber, the exterior surface of the chamber, the interior        chamber wall, the equilibration member within the chamber, and        the space within the chamber being divided into an upper portion        above the bisecting plane and a lower portion below the        bisecting plane;    -   the space within the upper portion of the chamber being in        liquid (fluid) and gas communication with the space within the        lower portion of the chamber via one or more gaps between the        equilibration member and the interior chamber wall;    -   a liquid inlet located in the upper portion of the chamber        positioned such that a liquid introduced into the chamber from        the liquid inlet contacts the upper portion of the outer surface        of the equilibration member;    -   a liquid outlet located in the lower portion of the chamber        positioned to permit outflow of some or all of the liquid        introduced into the chamber that collects in the lower portion        of the chamber by gravity;    -   a gas inlet located in the wall of the lower portion of the        chamber; and    -   a gas outlet located in the wall (e.g., in the is        removably-resealable portion of chamber) of the upper portion of        the chamber;        wherein at least a section of the upper portion of the chamber        wall is removably-resealable to the remainder of the upper        surface and/or the outer wall.-   2. The apparatus of embodiment 1 wherein the equilibration member is    selected from the group consisting of: a spheroid; an ellipsoid, an    ovoid; a hemisphere; a hemiellipsoid; a hemiovoid; a domed frustum;    a series (two, three, four, or more) of spheres or disks aligned    along the central axis (see, e.g., FIGS. 5A-5N and 6A-6N); a column;    a column having one, two, three, four, or more spiral grooves; a    column having sinusoidal oscillating sides; a cone having one, two,    three, four, or more spiral grooves; and a cone having sinusoidal    oscillating sides.-   3. The apparatus of any preceding embodiment wherein the interior    and/or exterior surface of the chamber is substantially in the form    of a vertical right cylinder, a sphere, an ellipsoid, or an ovoid.-   4. The apparatus of any preceding embodiment, wherein the chamber is    a substantially vertical right cylinder (VRC) wherein the wall forms    an upper and a lower surface positioned substantially perpendicular    to the central axis of the chamber.-   5. The apparatus of any preceding embodiment, wherein the section of    the upper portion of the wall that is removably-resealable forms a    lid on the remainder of the lower portion of the chamber,    -   wherein when the chamber is a VRC with an upper surface        positioned substantially perpendicular to the central axis of        the chamber, the lid comprises all or part of the upper surface.-   6. The apparatus of embodiment 5, wherein the liquid inlet and/or    gas outlet are positioned in the lid.-   7. The apparatus of any preceding embodiment, wherein the liquid    inlet is positioned either at, or proximate to, the central axis.-   8. The apparatus of any preceding embodiment, wherein when the    chamber is a VRC with a lower surface positioned substantially    perpendicular to the central axis of the chamber the liquid outlet    and/or the gas inlet are positioned in the lower surface of the    chamber.-   9. The apparatus of any preceding embodiment, wherein the liquid    outlet is positioned in the lower portion of the outer wall of the    chamber; wherein the liquid outlet is of an adjustable diameter to    accommodate a range of liquid flow rates, and wherein liquid flowing    through the outlet creates a seal that limits gas from entering or    exiting the equilibrium chamber by way of the liquid outlet thereby    forming a self-correcting pressure seal that equalizes the interior    and exterior pressure to substantially match ambient barometric    pressure.-   10. The apparatus of embodiment 9, wherein the gas inlet 3 is    positioned in the wall of the chamber w at a level between the    bisecting plane of the equilibration member when located in the    chamber and a plane that is perpendicular to the central axis and    parallel to a plane passing through the liquid outlet 2 (see, e.g.,    FIG. 2 or 3).-   11. The apparatus of any preceding embodiment, wherein the gas    outlet is positioned in the removably-resealable portion of the    chamber wall (e.g., in the flat upper surface of a VRC lid).-   12. The apparatus of any one of embodiments 1-10, wherein, when the    chamber is a VRC, the gas outlet is not located in the    removably-resealable portion of the chamber wall.-   13. The apparatus of any preceding embodiment, wherein the liquid    inlet comprises a liquid inlet nozzle (e.g., a piece of tubing) that    extends into the chamber.-   14. The apparatus of any preceding embodiment, wherein the liquid    inlet nozzle extends into the chamber at a level that is between the    upper surface (top moist point) of the equilibration member and a    plane that is parallel to the bisecting plane and passes through the    gas outlet.-   15. The apparatus of any preceding embodiment, wherein the surface    of the equilibration member is not porous and/or does not absorb    water.-   16. The apparatus of any preceding embodiment, wherein the surface    of the equilibration member is hydrophilic.-   17. The apparatus of any preceding embodiment, wherein the interior    surface of the chamber has a contact angle with water greater than    about 70°, 80°, 90°, 100°, 110°, 120°, 130°, or 140° at 22° C.-   18. The apparatus of any preceding embodiment, wherein the interior    surface of the chamber has a slide angle with water less than about    30°, 20°, 10°, or 5° at 22° C.-   19. The apparatus of any preceding embodiment, wherein the gas inlet    comprises an opening that directs the incoming gas in the direction    of the central axis or into a plane that is perpendicular to the    central axis of the chamber.-   20. The apparatus of any of embodiments 1-15, wherein the gas inlet    comprises an opening that directs the incoming gas substantially in    a plane that is perpendicular to the central axis (e.g., forcing the    gas to circulate in a clockwise or counter clockwise fashion with    the chamber).-   21. The apparatus of any preceding embodiment, wherein:    -   i) the equilibrium member is free to floating on liquid that        accumulates in the lower portion of the chamber (the accumulated        liquid acts as a liquid bearing and the equilibrium member may        freely rotate under the force of the liquid entering the chamber        such as via the inlet nozzle(s) described in embodiments 13 and        14); or    -   ii) the apparatus further comprising an annular element within        the chamber in contact with the lower portion of the chamber        (e.g., the substantially planar lower surface of a VRC) and the        equilibration member.-   22. The apparatus of any preceding embodiment, wherein the    equilibration member comprises a magnet or a magnetically    susceptible material, and wherein the apparatus further comprises a    magnet or magnetically susceptible material positioned on or in the    chamber wall so as to magnetically engage the equilibration member    (e.g., hold the member in position within the chamber by contacting    the member to the chamber wall or proximate to the chamber wall).-   23. The apparatus of embodiment 22, wherein when the equilibration    member is magnetically engaged it is positioned proximate to, but    not in direct contact with, the lower portion of the chamber wall    (e.g., when the chamber is a VRC the equilibration member is held    against a support such as the annular element of embodiment 21 which    is in contact with the substantially planer lower surface of the    cylinder).-   24. The apparatus of any one of embodiments 22 or 23, wherein the    central axis of the chamber passes through the magnet or    magnetically susceptible material positioned on or in the wall of    the chamber.-   25. The apparatus of any preceding embodiment, wherein the volume of    the chamber is less than 2.5 times (e.g., less than 2.25, 2.0, 1.75,    1.6, 1.5, 1.4, 1.3, 1.2 or 1.1 times) the volume of the    equilibration member.-   26. A method of determining the amount of a gas or gases of interest    present in a liquid comprising the following steps:    -   i) providing an apparatus of any one of embodiments 1-25;    -   ii) introducing the liquid into the chamber of the apparatus by        way of the liquid inlet such that it passes over the        equilibration member thereby forming a falling film over all or        part of the equilibration member's surface, and exits the        apparatus by way of the liquid outlet;    -   iii) directing a carrier gas into the apparatus by way of the        gas inlet such that it flows over the equilibration member in a        direction that is counter current to the flow of the liquid and        exits the chamber of the apparatus by way of the gas outlet;    -   iv) directing all or part of the gas that exits the chamber to a        sensor of an analytical instrument that determines the amount of        the gas or gases of interest present in the liquid; and    -   v) determining the amount of a gas or gases of interest present        in the liquid based on the output of the detection system.-   27. The method of embodiment 26, wherein the carrier gas is selected    from the group consisting of air, nitrogen, an inert gas (e.g.,    argon, neon, xenon, or helium), hydrogen, oxygen or a mixture of any    thereof.-   28. The method of any one of embodiments 26 to 27, wherein at least    one of the gas or gases of interest is selected from the group    consisting of ammonia, CO₂, CO, sulfur oxides (sulfur dioxide),    nitrogen oxides (e.g., NO or NO₂), methane, ethane, hydrocarbons,    halogenated hydrocarbons, chlorofluorocarbons (CFCs),    hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), esters, sulfur    hexafluoride (SF₆), chlorine, bromine, radon, hydrogen sulfide    (H₂S), HF, HCl, HBr, and HI.-   29. The method of any one of embodiments 26 to 28, wherein the gas    of interest is CO₂.-   30. The method of any one of embodiments 26 to 29, wherein the    liquid comprises water.-   31. The method of any one of embodiments 26 to 30, wherein the    liquid is selected from the group consisting of: salt water, sea    water, brackish water, tidal water, marsh water, river water, lake    water, stream water, spring water, ground water, aquifer water, pore    water, geyser water, volcanic water, well water, swimming pool    water, aquarium water, sewer water, industrial waste water,    irrigation water, run-off from agricultural sites, run-off from    mines, run-off from industrial sites, drinking water treatment plant    water, and sewage treatment water.-   32. The method of any one of embodiments 26 to 31, wherein the    liquid comprises water, and wherein directing all or part of the gas    that exits the chamber to a detection system further comprises    providing a dryer/dehumidifier positioned between the gas outlet and    the detection system, the dryer/dehumidifier receiving all or part    of the gas that exits the chamber and removing all or part of the    water vapor from the gas exiting the chamber to produce a dried gas    stream, the detection system receiving all or part of the dried gas    stream.-   33. The method of any one of embodiments 26 to 32 further comprising    step (vi):    -   vi) for a period of time flowing gas through the sensor and/or        dryer/dehumidifier to remove all or part of the condensed liquid        vapor (e.g., water vapor) that may have condensed in the sensor        and/or dryer/dehumidifier, or in the lines connected thereto.-   34. The method of any one of embodiments 26 to 33, wherein the    apparatus further comprises an auto-controlled drying mechanism    comprising a sampling port circuit composed of a combination of    solenoids, valves, and a mechanism (e.g., relay, sensor, and/or    switch) to stop liquid pumping into the chamber, the method further    comprising:    -   stopping test liquid (e.g., water) from flowing into the        equilibrator,    -   operating the auto-controlled drying mechanism to cause carrier        gas flow from a port [which can draw or vent a gas to the        atmosphere (air), a carrier gas source, and/or calibrator gas        source such as ports 20 or 21] through the dryer/dehumidifier 9,        or the dryer/dehumidifier 9 and the sensor 16, toward the        equilibrator (e.g., reverse flow) through a sample gas line 8        (which during forward flow brings gas from the equilibrator to        the sensor system); and    -   exhausting the gas flowing from the port after passing through        the dryer/dehumidifier, or the dryer/dehumidifier and the        sensor, through a port 19 prior to reaching the equilibrator E        and/or after passing through the equilibrator chamber 22.        (Passing carrier gas through the parts of the system including        the gas sample line, and exhausting the gas once laden vapors of        condensed liquid, removes condensation in the gas sample line        between the equilibrator and the sensor system, thereby        preventing system failure due to condensed liquid (e.g., water)        entering into the sensor system.)-   35. The method of any one of embodiments 26 to 34, wherein during    the period when a carrier gas (e.g., air and/or calibrator gas) is    flowing (e.g., from a port such as 20 or 21) through the sensor 16,    establishing a baseline measurement and/or calibration measurement.-   36. The method of embodiment 35, wherein the calibrator gas is air    and the flow of liquid is stopped at the liquid inlet.-   37. The method of embodiment 35, wherein the calibrator gas has a    defined amount of CO₂ and the flow of liquid is stopped at the    liquid inlet.-   38. The method of any one of embodiments 26 to 37, further    comprising:    -   providing a gas with a known amount of the gas of interest;    -   introducing said gas with a known amount of the gas of interest        into the gas inlet (e.g., through port 22) and passing it        through the equilibrator (and the dryer/dehumidifier if present)        and the sensor, and then exhausting it from the system after        passing through the sensor (e.g., through port 21)        (alternatively, introducing said gas with a known amount of the        gas of interest into the sensor (e.g., through port 19 or port        20) and exhausting it from the system after passing through the        sensor (e.g., through port 21)); and    -   calibrating and/or confirming the calibration of the detection        system while the gas with a known amount of the gas of interest        is present in and/or flowing through the sensor.-   39. The method of any one of embodiments 26 to 34, further    comprising:    -   providing a liquid with a known amount of the gas of interest,    -   introducing said liquid with a known amount of the gas of        interest into the liquid inlet; and    -   calibrating and/or confirming the calibration of the detection        system while the liquid with a known amount of the gas of        interest is flowing through the equilibrator.

EXAMPLES Example 1. Comparison of Equilibrators with 20 and 25 cmDiameter Equilibration Members

Two equilibrators having spherical equilibration members placed insideVRC chambers with a single fluid inlet in the center of their removableplanar upper surface and outlet on the cylindrical surface about 1-1.5cm from the bottom of the chamber were prepared (see, e.g., FIG. 3). Thefirst equilibrator had an equilibration member had a sphericalequilibration member about 20.3 cm (about 8 inches) in diameter with achamber volume of about 7.57 liters (about 2 gallons). The secondequilibration member had a spherical equilibration member about 25.4 cm(about 10 inches) in diameter with a chamber volume of about 13.25liters (about 3.5 gallons).

Using a semi-enclosed 400 liter tank, water was pumped from the bottomof the tank into the tops of the two falling film equilibrators inparallel and at similar flow rates. CO₂ concentrations in the test tankwere manipulated by either spiking with pure CO₂ gas momentarily, or bycontinual bubbling with CO₂—stripped gas to drive CO₂ concentrationsdownward. Water flow rates ranged from approximately 50 to 100 gallonsper minute. Water draining out the bottom of the equilibrator weredirected back into the tank and were recirculated. At any time, one orthe other of the paired equilibrators was connected via a valve systemto a closed loop gas train that led out of the top of the equilibratorchamber, through a dehumidifying apparatus, into a LI-COR LI-7000infrared CO₂/H₂O gas analyzer and back into the bottom of theequilibrator. Air was used as the carrier gas and was circulated in theclosed loop gas train at a rate of 1 liter per minute. Readings of pCO₂were logged at 1-min intervals. The gas train was switched rapidly toalternately monitor the gas flow and determine how closely twoequilibrators of different size agreed with one another when challengedwith water of the exact same CO₂ content and to observe how quickly theyresponded to changes in dissolved gas (CO₂).

FIG. 9 shows a performance comparison of the equilibrators having an8-inch diameter spherical equilibration member with the equilibratorhaving a 10-inch dimeter equilibration member over a 6-day period. The10-inch and 8-inch equilibrators were connected to the gas analyzerrepeatedly and over a wide variety of CO₂ concentrations ranging fromwell below atmospheric concentrations to over 1200 ppmv. In allinstances, the 8-inch and 10-inch equilibrators were in near exactagreement of one another.

Example 2. Comparison of Equilibrators with 20 and 9 cm DiameterEquilibration Members

The experiment described in Example 1 was repeated using the firstequilibrator from Example 1 with an equilibration member having adiameter of about 20.3 cm (about 8 inches) and a chamber volume of about7.57 liters (about 2 gallons). For this example the second equilibratorhad a spherical equilibration member about 9.4 cm (3.7 inches) indiameter and a VRC chamber with a volume of about 1 liter (0.26gallons). As in Example 1, the resulting measurements show a very highdegree of agreement between the two equilibrators.

These and a variety of other tests of the falling film liquid-gasequilibrators described herein across broad ranges of gas (e.g., CO₂)concentrations, liquid (e.g., water) and carrier gas (e.g., air) flowrates indicate that falling film equilibrators as described herein havethe ability to produce consistent, precise, and accurate dissolved gasmeasurement (e.g., dissolved pCO₂ measurements) even acrosssignificantly different equilibrator dimensions. The convergence of thetest results using equilibrators of different size suggests thatcomplete equilibration is achieved in each case, as opposed to somearbitrary level(s) of incomplete air-water equilibration.

Example 3. Test of Equilibrator Accuracy—Equilibrium Measurements ofWater Enriched with Standard Gas CO₂/Air Mixtures

A 9 cm diameter equilibrator with a VRC chamber with a volume of about 1liter (0.26 gallons) was attached via water- and air-tight connectors toa 5-gallon water chamber such that the system was fully closed off fromthe surrounding ambient atmosphere. The water chamber was enriched bybubbling the water with a certified standard CO₂/air mixture. Once thewater chamber was fully enriched with the standard gas, the gas wasturned off and the equilibrator was turned on. Enriched water was pumpedover the equilibrator member, forming a falling film, and then drainedback into the enriched water chamber. Equilibration was fully achievedafter 9 minutes of run time (5 τ) and the equilibrator headspace CO₂concentration was measured as 7578±12.2 ppmv (mean±1 SD, n=29). Thisresult agreed closely with the certified standard gas nominalconcentration (7579 ppmv±1%), and equilibration remained stable for 30additional minutes, until the equilibrator was turned off. This resultindicates that the 9 cm diameter equilibrator equilibrates both quicklyand fully (i.e., a stable equilibration with a known target standard wasattained by the previously measured time constants.

1. An apparatus comprising: a chamber comprising an outer wall that isdisposed substantially symmetrically about a central axis, the outerwall defining the interior surface of the chamber, the exterior surfaceof the chamber, and space within the chamber; an equilibration memberwithin the chamber having an equilibration member surface, an axis ofrotation, and a bisecting plane perpendicular to the axis of rotationpositioned at the midpoint of the equilibration member's axis ofrotation; the equilibration member being positioned within the chambersuch that its axis of rotation and the central axis of the chambercoincide or substantially coincide; the chamber, the exterior surface ofthe chamber, the interior chamber wall, the equilibration member withinthe chamber, and the space within the chamber being divided into anupper portion above the bisecting plane and a lower portion below thebisecting plane; the space within the upper portion of the chamber beingin liquid (fluid) and gas communication with the space within the lowerportion of the chamber via one or more gaps between the equilibrationmember and the chamber wall; a liquid inlet located in the upper portionof the chamber positioned such that a liquid introduced into the chamberfrom the liquid inlet contacts the upper portion of the outer surface ofthe equilibration member; a liquid outlet located in the lower portionof the chamber positioned to permit outflow of some or all of the liquidintroduced into the chamber that collects in the lower portion of thechamber by gravity; a gas inlet located in the wall of the lower portionof the chamber; and a gas outlet located in the wall of the upperportion of the chamber; wherein at least a section of the upper portionof the chamber wall is removably-resealable to the remainder of theupper surface and/or the outer wall.
 2. The apparatus of claim 1 whereinthe equilibration member is selected from the group consisting of: aspheroid; an ellipsoid, an ovoid; a fusiform shape; a hemisphere; ahemiellipsoid; a hemiovoid; a domed frustum; a series (two, three, four,or more) of spheres or disks aligned along the central axis; a column; acolumn having one, two, three, four, or more spiral grooves; a columnhaving sinusoidal oscillating sides; a cone having one, two, three,four, or more spiral grooves; and a cone having sinusoidal oscillatingsides.
 3. The apparatus of claim 2 wherein the interior and/or exteriorsurface of the chamber is substantially in the form of a vertical rightcylinder, a sphere, an ellipsoid, or an ovoid.
 4. The apparatus of claim3, wherein the chamber is a substantially vertical right cylinder (VRC)wherein the wall forms an upper and a lower surface positionedsubstantially perpendicular to the central axis of the chamber.
 5. Theapparatus of claim 4, wherein the section of the upper portion of thewall that is removably-resealable forms a lid on the chamber, whereinwhen the chamber is a VRC with an upper surface positioned substantiallyperpendicular to the central axis of the chamber, the lid comprises allor part of the upper surface.
 6. The apparatus of claim 5, wherein theliquid inlet is positioned in the lid.
 7. The apparatus of claim 6,wherein the liquid inlet is positioned either at, or proximate to, thecentral axis.
 8. The apparatus of claim 6, wherein, when the chamber isa VRC with a lower surface positioned substantially perpendicular to thecentral axis of the chamber, the liquid outlet and/or the gas inlet arepositioned in the lower surface of the chamber.
 9. The apparatus ofclaim 6, wherein the liquid outlet is positioned in the lower portion ofthe outer wall of the chamber, wherein the liquid outlet is of anadjustable diameter to accommodate a range of liquid flow rates, andwherein liquid flowing through the outlet creates a seal that limits gasfrom entering or exiting the equilibrium chamber by way of the liquidoutlet thereby forming a self-correcting pressure seal that equalizesthe interior and exterior pressure to substantially match ambientbarometric pressure.
 10. The apparatus of claim 9, wherein the gas inletis positioned in the wall of the chamber at a level between thebisecting plane of the equilibration member in the chamber and a planethat is perpendicular to the central axis and parallel to a planepassing through the liquid outlet.
 11. The apparatus of claim 10,wherein the gas outlet is positioned in the removably-resealable portionof the chamber wall.
 12. The apparatus of claim 1, wherein, when thechamber is a VRC, the gas outlet is not located in theremovably-resealable portion of the chamber wall. 13.-14. (canceled) 15.The apparatus of claim 1, wherein the surface of the equilibrationmember is not porous and/or does not absorb water; and wherein thesurface of the equilibration member is hydrophilic.
 16. (canceled) 17.The apparatus of claim 1, wherein the interior surface of the chamberhas a contact angle with water greater than about 70°, 80°, 90°, 100°,110°, 120°, 130°, or 140° at 22° C.; or wherein the interior surface ofthe chamber has a slide angle with water less than about 30°, 20°, 10°,or 5° at 22° C. 18.-20. (canceled)
 21. The apparatus of claim 1: furthercomprising an annular element within the chamber in contact with thelower portion of the chamber and the equilibration member; or whereinthe equilibration member comprises a magnet or a magneticallysusceptible material, and wherein the apparatus further comprises amagnet or magnetically susceptible material positioned on or in thechamber wall so as to magnetically engage the equilibration member.22-24. (canceled)
 25. The apparatus of claim 1, wherein the volume ofthe chamber is less than 2.5 times the volume of the equilibrationmember.
 26. A method of determining the amount of a gas or gases ofinterest present in a liquid comprising the following steps: i)providing an apparatus of claim 1; ii) introducing the liquid into thechamber of the apparatus by way of the liquid inlet such that it passesover the equilibration member, thereby forming a film over all or partof the equilibration member's surface, and exits the apparatus by way ofthe liquid outlet; iii) directing a carrier gas into the apparatus byway of the gas inlet such that it flows over the equilibration member ina direction that is counter current to the flow of the liquid and exitsthe chamber of the apparatus by way of the gas outlet; iv) directing allor part of the gas that exits the chamber to a sensor of an analyticalinstrument that determines the amount of the gas or gases of interestpresent in the liquid; and v) determining the amount of a gas or gasesof interest present in the liquid based on the output of the detectionsystem.
 27. The method of claim 26, wherein the carrier gas is selectedfrom the group consisting of air, nitrogen, an inert gas, hydrogen,oxygen or a mixture of any thereof; and wherein at least one of the gasor gases of interest is selected from the group consisting of ammonia,CO₂, CO, sulfur oxides, nitrogen oxides, methane, ethane, hydrocarbons,halogenated hydrocarbons, chlorofluorocarbons (CFCs), hydrofluorocarbons(HFCs), perfluorocarbons (PFCs), esters, sulfur hexafluoride (SF₆),chlorine, bromine, radon, hydrogen sulfide (H₂S), HF, HCl, HBr, and HI.28. (canceled)
 29. The method claim 26, wherein the gas of interest isCO₂.
 30. The method of claim 29, wherein the liquid comprises water.31-39. (canceled)